The Microcontroller Architecture, Programming And kaz-news.info architecture, programming, and applications / Kenneth J. Ayala. p. cm. Readers will be trained on programming the Intel microcontroller, one of the most integrated development software that is included at the back of the book. Search results. 14 results for Books: "Kenneth Ayala" The Microcontroller & Embedded Systems Using Assembly and C with CD. by Kenneth.

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Ayala - The Micro Controller - Free ebook download as PDF File .pdf), Text File .txt) or read book online for free. all about microcontrollers. Ayala. *21* The Microcontroller. LUKIS and applications / Kenneth J. Ayala. p. cm. Includes index. both of whom made this book possible . The Microcontroller book. Read reviews from world's largest community for readers. Gain valuable assembly code programming knowledge with the help o.

This gal- axy o f parts, the result o f desires b y the manufacturers to leave no market niche unfilled, would require many chapters to cover. I n this chapter, we w i l l study a "generic" , housed i n a pin DIP, and direct the investigation o f a particular type to the data books.

The block diagram o f the i n Figure 2. The figure also shows the usual CPU components: Four register banks, each containing eight registers Sixteen bytes, which may be addressed at the bit level Eighty bytes of general-purpose data memory Thirty-two inputloutput pins arranged as four 8-bit ports: PO-P3 Two bit timerlcounters: TO and T1 Full duplex serial data receiverltransmitter: SBUF Control registers: These registers and memory locations can be made to operate using the software instructions that are incorporated as part of the design.

The program instructions have to do with the control of the registers and digital data paths that are physically contained inside the , as well as memory locations that are physically located outside the The model is complicated by the number of special-purpose registers that must be present to make a microcomputer a microcontroller.

A cursory inspection of the model is recommended for the first-time viewer; return to the model as needed while progressing through the remainder of the text. Most of the registers have a specific function; those that do occupy an individual block with a symbolic name, such as A or THO or PC.

Others, which are generally indis- tinguishable from each other, are grouped in a larger block, such as internal ROM or RAM memory. Each register, with the exception of the program counter, has an internal 1-byte ad- dress assigned to it. That is, the entire byte of data at such register addresses may be read or altered, or individual bits may be read or altered.

Software instructions are gener- ally able to specify a register by its address, its symbolic name, or both. A pinout of the packaged in a pin DIP is shown in Figure 2. It is important to note that many of the. For this reason. Alternate functions are shown b e l o w the p o r t name in parentheses. Pin n u m - bers and pin names are shown inside the DIP package.

Not all of the possible features may be used at the same time. For example, port 3 bit 0 abbreviated P3. The system designer decides which of these two functions is to be used and designs the hard- ware and software affecting that pin accordingly.

The Oscillator and Clock The heart of the is the circuitry that generates the clock pulses by which all internal operations are synchronized. Typically, a quartz crystal and capacitors are em- ployed, as shown in Figure 2. The crystal frequency is the basic internal clock fre- quency of the microcontroller. The manufacturers make available designs that can run at specified maximum and minimum frequencies, typically 1 megahertz to 16 mega- hertz. Minimum frequencies imply that some internal memories are dynamic and must always operate above a minimum frequency, or data will be lost.

Communication needs often dictate the frequency of the oscillator due to the require- ment that internal counters must divide the basic clock rate to yield standard communica- tion bit per second baud rates. If the basic clock frequency is not divisible without a remainder. Ceramic resonators may be used as a low-cost alternative to crystal resonators. How- ever, decreases in frequency stability and accuracy make the ceramic resonator a poor choice if high-speed serial data communication with other systems, or critical timing, is to be done.

The oscillator formed by the crystal, capacitors, and an on-chip inverter generates a pulse train at the frequency of the crystal, as shown in Figure 2. The clock frequency, f. The smallest interval of time to accomplish any simple instruction, or part of a complex instruction, however, is the machine cycle. The machine cycle is itself made up of six states. A state is the basic time interval for discrete operations of the microcontroller such as fetching an opcode byte, decoding an opcode, executing an opcode, or writing a data byte.

Two oscillator pulses define each state. Program instructions may require one, two, or four machine cycles to be executed, depending on the type of instruction. Instructions are fetched and executed by the micro- controller automatically, beginning with the instruction located at ROM memory address OOOOh at the time the microcontroller is first reset.

To calculate the time any particular instruction will take to be executed, find the num- ber of cycles, C, from the list in Appendix A. The time to execute that instruction is then found by multiplying C by 12 and dividing the product by the crystal frequency: A 12 megahertz crystal yields the con- venient time of one microsecond per cycle.

An Program Counter and Data Pointer The contains two bit registers: Each is used to hold the address of a byte in memory. Program instruction bytes are fetched from locations in memory that are addressed by the PC. The PC is automatically incremented after every instruction byte is fetched and may also be altered by certain instructions. The PC is the only register that does not have an internal address.

Two of these, registers A and B, comprise the mathematical core of the central processing unit CPU. The A accumulator register is the most versatile of the two CPU registers and is used for many operations, including addition, subtraction, integer multiplication and divi- sion, and Boolean bit manipulations. The A register is also used for all data transfers be- tween the and any external memory. The B register is used with the A register for multiplication and division operations and has no other function other than as a location where data may be stored.

Other instructions can test the condition of the flags and make decisions based upon the Rag states. In order that the flags may be conveniently addressed, they are grouped inside the program status word PSW and the power control PCON registers. The has four math flags that respond automatically to the outcomes of math operations and three general-purpose user flags that can be set to I or cleared to 0 by the programmer as desired.

Note that all of the flags can he set and cleared by the programmer at will. The math flags, however. The program status word is shown in Figure 2. The PSW contains the math Rags, user program flag FO, and the register select bits that identify which of the four general- purpose register banks is currently in use by the program. Detailed descriptions of the math flag operations will be discussed in chapters that cover the opcodes that affect the flags. The user flags can be set or cleared using data move instructions covered in Chapter 3.

Additional memory can be added externally using suitable circuits. Unlike microcontrollers with Von Neumann architectures, which can use a single memory address for either program code or data, but not,for both, the 1 has a Harvard architecture, which uses the same address, in different memories, for code and data.

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In- ternal circuitry accesses the correct memory based upon the nature of the operation in progress. Thirty-two bytes from address OOh to IFh that make up 32 working registers or- ganized as four banks of eight registers each. The four register banks are num- bered O to 3 and are made up of eight registers named RO to R7. Each register can be addressed by name when its bank is selected or by its RAM address.

Thus RO of bank 3 is RO if bank 3 is currently selected or address 18h whether bank 3 is selected or not. Register banks not selected can be used as general-purpose RAM. Bank 0 is selected upon reset. A bit-addressable area of 16 bytes occupies RAM byte addresses 20h to 2Fh, forming a total of addressable bits. An addressable bit may be specified by its bit address of OOh to 7Fh, or 8 bits may form any byte address from 20h to 2Fh.

Thus, for example, bit address 4Fh is also bit 7 of byte address 29h. Ad- dressable bits are useful when the program need only remember a binary event switch on, light off, etc. Internal RAM is in short supply as it is, so why use a byte when a bit will do?

A general-purpose RAM area above the bit area, from 30h to 7Fh, addressable as bytes. The Stack and the Stack Pointer The stack refers to an area of internal RAM that is used in conjunction with certain op- codes to store and retrieve data quickly. The 8-bit stack pointer SP register is used by the to hold an internal RAM address that is called the "top of the stack.

When data is to be placed on the stack, the SP increments before storing data on the stack so that the stack grows up as data is stored. As data is retrieved from the stack, the byte is read from the stack, and then the S P decrements to point to the next available byte of stored data. Operation of the stack and the SP is shown in Figure 2. The SP is set to 07h when the is reset and can be changed to any internal RAM address by the programmer.

The stack is limited in height to the size of the internal RAM. The stack has the poten- tial if the programmer is not careful to limit its growth to overwrite valuable data in the register banks, bit-addressable RAM, and scratch-pad RAM areas. The programmer is responsible for making sure the stack does not grow beyond pre-defined bounds!

The stack is normally placed high in internal RAM, by an appropriate choice of the number placed in the SP register. StoringData on the Stack m Address This feature allows the programmer to change only what needs to be altered, leaving the remaining bits in that SFR unchanged. Not all o f the addresses from 80h to FFh are used for SFRs, and attempting to use an address that is not defined, or "empty," results in unpredictable results.

I n Figure 2. Failure to use this number convention will result in an assembler error when the program is assembled. Internal ROM The is organized so that data memory and program code memory can be in two entirely different physical memory entities. Each has the same address ranges. The structure of the internal RAM has been discussed previously. Program addresses higher than OFFFh, which exceed the inter- nal ROM capacity, will cause the to automatically fetch code bytes from external program memory.

As noted in Chapter I , microprocessor designs must add additional chips to interface with external circuitry; this ability is built into the microcontroller. To be commercially viable, the had to incorporate as many functions as were technically and economically feasible. The main constraint that limits numerous functions is the number of pins available to the circuit designers. The DIP has 40 pins, and the success of the design in the marketplace was determined by the flexibility built into the use of these pins.

For this reason, 24 of the pins may each be used for one of two entirely different functions, yielding a total pin configuration of The function a pin performs at any given instant depends, first, upon what is physically connected to it and, then, upon what software commands are used to "program" the pin. Both of these factors are under the complete control of the programmer and circuit designer.

Given this pin flexibility, the may be applied simply as a single component with only, or it may be expanded to include additional memory, parallel ports, and serial data communication by using the alternate pin assignments. The key to programming an alternate pin function is the port pin circuitry shown in Figure 2.

Each port has a D-type output latch for each pin. For in- stance, the eight latches for port 0 are addressed at location 80h; port 0 pin 3 is bit 2 of the PO SFR. The port latches should not be confused with the port pins; the data on the latches does not have to be the same as that on the pins. The two data paths are shown in Figure 2. The top buffer is enabled when latch data is read, and the lower buffer, when the pin state is read. The status of each latch may be read from a latch buffer, while an input buffer is connected directly to each pin so that the pin status may be read independently of the latch state.

Different opcodes access the latch or pin states as appropriate. Port operations are determined by the manner in which the is connected to external circuitry.

Programmable port pins have completely different alternate functions. The configura- tion of the control circuitry between the output latch and the port pin determines the nature of any particular port pin function. An inspection of Figure 2. The ports are not capable of driving loads that require currents in the tens of milli- amperes mA.

As previously mentioned. An example range of logic-level currents, volt- ages, and total device power requirements is given in the following table:. CMOS 2. OV 10pA mW. These figures tell us that driving more than two LSTTL inputs degrades the noise immunity of the ports and that careful attention must be paid to buffering the ports when they must drive currents in excess of those listed. Again, one must refer to the manufac- turers' data books when designing a "real" application.

Port 0 Port 0 pins may serve as inputs. For example, when a pin is to be used as an input, a I must be written to the corresponding port 0 latch by the program, thus turn- ing both of the output transistors off, which in turn causes the pin to "float" in a high- impedance state, and the pin is essentially connected to the input buffer. When used as an output, the pin latches that are programmed to a 0 will turn on the lower FET, grounding the pin.

All latches that are programmed to a 1 still float; thus, external pullup resistors will be needed to supply a logic high when using port 0 as an output. When port 0 is used as an address bus to external memory, internal control signals switch the address lines to the gates of the Field Effect Transistories FETs.

After the address has been formed and latched into external circuits by the Address Latch Enable ALE pulse, the bus is turned around to become a data bus. Port 0 now reads data from the external memory and must be configured as an input, so a logic 1 is automatically written by internal control logic to all port 0 latches. Port 1 Port I pins have no dual functions. Used as an input, a I is written to the latch, turning the lower FET off; the pin and the input to the pin buffer are pulled high by the FET load.

An external circuit can overcome the high impedance pullup and drive the pin low to input a 0 or leave the input high for a 1. If used as an output, the latches containing a I can drive the input of an external circuit high through the pullup. If a 0 is written to the latch, the lower FET is on, the pullup is off, and the pin can drive the input of the external circuit low.

To aid in speeding up switching times when the pin is used as an output, the internal FET pullup has another FET in parallel with it. The second FET is turned on for two oscillator time periods during a low-to-high transition on the pin, as shown in Figure 2.

This arrangement provides a low impedance path to the positive voltage supply to help reduce rise times in charging any parasitic capacitances in the external circuitry. Port 2 Port 2 may be used as an inputloutput port similar in operation to port 1. The alternate use of port 2 is to supply a high-order address byte in conjunction with the port 0 low-order byte to address external memory.

Port 2 pins are momentarily changed by the address control signals when supplying the high byte of a bit address. Port 2 latches remain stable when external memory is addressed, as they do not have to be turned around set to 1 for data input as is the case for port 0.

Port 3 Port 3 is an inputloutput port similar to port I. The input and output functions can be programmed under the control of the P3 latches or under the control of various other spe- cial function registers. The port 3 alternate uses are shown in the following table: Unlike ports 0 and 2, which can have external addressing functions and change all eight port bits when in alternate use, each pin of port 3 may be individually programmed to be used either as or as one of the alternate functions.

Internal control circuitry accesses the correct physical memory, depending upon the machine cycle state and the opcode being executed. There are several reasons for adding external memory, particularly program memory, when applying the in a system.

When the project is in the prototype stage, the expense-in time and money-of having a masked internal ROM made for each program "try" is prohibitive. To alleviate this problem. The resulting circuit board layout will be identical to one that uses a factory-programmed 1. The only drawbacks to the are the specialized EPROM programmers that must be used to program the non-standard pin part, and the limit of "only" bytes of program code.

The solution works well if the program will fit into 4K bytes. Unfortunately, many times, particularly if the program is written in a high-level language, the program size exceeds 4K hytes, and an external program memory is needed.

Again, the manufac- turers provide a version for the job, the ROMless External RAM. External RAM, up to 64K bytes, may also be added to any chip in the family. Connecting External Memory Figure 2. The accesses exter- nal RAM whenever certain program instructions are executed.

Figure 2. Dur- ing any memory access cycle, port 0 is time multiplexed. That is, it first provides the lower byte of the bit memory address, then acts as a bidirectional data bus to write or read a byte of memory data. Port 2 provides the high byte of the memory address during the entire memory readlwrite cycle.

The lower address byte from port 0 must be latched into an external register to save the byte. Address byte save is accomplished by the ALE clock pulse that provides the correct timing for the ' type data latch. The port 0 pins then become free to serve as a data bus. Port 2 A15 I I.

Enable Read Write Pulse. Set when timer rolls from all ones to zero. Cleared when processor vectors to execute Interrupt service routlne located at program address Bh. Set to 1 by program to enable timer to count; cleared to 0 by program to halt timer. Does not reset timer. Cleared when processor vectors to execute interrupt service routine located at program address Bh.

The Microcontroller Kenneth J Ayala

Set to 1 by program to enable tlmer to count; cleared to 0 by program to halt timer. Set to 1 when a high to low edge stgnal IS received on port 3 pin 3. Not related to timer operations. Set to 1 by program to enable external interrupt 1 to be trtggered by a falling edge signal. Set to 0 by program to enable a low level signal on external interrupt t to generate an interrupt.

Set to 1 when a high to low edge signal is received on port 3 pln 3. Cleared when processor vectors to interrupt service routine located at program address h. Not related to timer operations Continued. Note that theWR and RD signals are alternate uses for port 3 pins 16 and Also, port O is used for the lower address byte and data; port 2 is used for upper address bits. The use o f external memory consumes many o f the port pins, leaving only port I and parts o f port 3 for general Counters and Timers Many microcontroller applications require the counting o f external events, such as the frequency o f a pulse train, or the generation o f precise internal time delays between com- puter actions.

Both o f these tasks can be accomplished using software techniques, but software loops for counting or timing keep the processor occupied so that other, perhaps more important, functions are not done. To relieve the processor o f this burden, two bit up counters, named TO and T I , are provided for the general use o f the programmer. Each counter may be programmed to count internal clock pulses.

Set to 1 by program to enable external interrupt 0 to be triggered by a falling edge signal. Set to 0 by program to enable a low level signal on external interrupt 0 to generate an interrupt. Bit addressable as TCON. Cleared to 0 by program to make timer act as a timer by counting internal frequency. Setlcleared by program to select mode. A l l counter action is controlled by bit states in the timer mode control register TMOD , the timerlcounter control register TCON , and certain program instructions.

TMOD is dedicated solely to the two timers and can be considered to be two duplicate 4-bit registers, each o f which controls the action o f one o f the timers. TCON has control bits and flags for the timers in the upper nibble, and control bits and flags for the external interrupts in the lower nibble. Timer Counter Interrupts The counters have been included on the chip to relieve the processor of timing and count- ing chores.

When the program wishes to count a certain number of internal pulses or external events, a number is placed in one o f the counters. The number represents the maximum count less the desired count, plus one. The counter increments from the initial number to the maximum and then rolls over to zero on the final pulse and also sets a timer flag. The flag condition may be tested by an instruction to tell the program that the count has been accomplished, or the flag may be used to interrupt the program.

As an example, if the crystal frequency is 6. The resultant timer clock is gated to the timer by means of the circuit shown in Figure 2. In other words, the counter is configured as a timer, then the timer - pulses are gated to the counter hy the run bit and the gate bit or the external input bits INTX.

As an example, the 6 megahertz oscillator frequency would result in a final frequency to TH of hertz. The timer flag would be set in. Pulse lnput lnterrupt Figure 2.

The timer flag is also set when TLX overflows. This mode exhibits an auto-reload feature: Timer Mode 3 Timers 0 and I may be programmed to be in mode 0 , I , or 2 independently of a similar mode for the other timer. This is not true for mode 3; the timers do not operate indepen- dently if mode 3 is chosen for timer 0. Timer 0 in mode 3 becomes two completely separate 8-bit counters.

TLO is controlled by the gate arrangement of Figure 2. Timer 1 may still be used in modes 0, 1, and 2. No interrupts will be generated by timer I while timer 0 is using the TFI overflow flag.

Switching timer I to mode 3 will stop it and hold whatever count is in timer 1.

Timer I can be used for baud rate generation for the serial port, or any other mode 0, 1, or 2 function that does not depend upon an interrupt or any other use of the TFI flag for proper operation. Counting The only difference between counting and timing is the source of the clock pulses to the counters.

When used as a timer, the clock pulses are sourced from the oscillator through the divide-byd circuit. When used as a counter. The input pulse on TX is sampled during P2 of state 5 every machine cycle. A change on the input from high to low between samples will increment the counter. Each high and low state of the input pulse must thus be held constant for at least one machine cycle to ensure reliable counting.

Since this takes 24 pulses, the maximum input frequency that can be accurately counted is the oscillator frequency divided by For our 6 megahertz crystal, the calculation yields a maximum external frequency of kilohertz. Serial Data InputIOutput Computers must he able to communicate with other computers in modern multiprocessor distributed systems. One cost-effective way to communicate is to send and receive data bits serially.

The has a serial data communication circuit that uses register SBUF to hold data. I connect to the serial data network.

SBUF is physically two registers. One is write only and is used to hold data to be transmitted out of the via TXD. The other is read only and holds received data from external sources via RXD.

Both mutually exclusive registers use address 99h. Baud rates are determined by the mode chosen. Serial Data Interrupts Serial data communication is a relatively slow process. Setlcleared by program to enable multiprocessor communications in modes 2 and 3. Clear to 0 if mode 0 is in use. Set to 1 to enable reception; cleared to 0 to dissable reception. Set to one at the end of bit 7 time in mode 0, and at the beginning of the stop bit for other modes.

Must be cleared by the program. Set to one at the end of bit 7 time in mode 0, and halfway through the stop bit for other modes. Set to 1 by program to double baud rate uslng timer 1 for modes 1, 2, and 3. Cleared to 0 by program to use timer 1 baud rate. PCON is not bit addressable. Notice that data transmission is under the complete control of the program, but reception of data is unpre- dictable and at random times that are beyond the control of the program.

These flags are ORed together to produce an interrupt to the pro- gram. The program must read these flags to determine which caused the interrupt and then clear the flag. This is unlike the timer flags that are cleared automatically; it is the respon- sibility of the programmer to write routines that handle the serial data flags.

TI is set to a I when the data has been transmitted and signifies that SBUF is empty for transmission purposes and that another data byte can be sent. If the program fails to wait for the TI Rag and overwrites SBUF while a previous data byte is in the process of being transmitted, the results will be unpredictable a polite term for "garbage out".

In addition, for mode 0 only.

Ayala - The Micro Controller

RI must be cleared to 0 also. Receiver interrupt Rag RI is set after data has been received in all modes. Setting REN is the only direct program control that limits the reception of unexpected data; the requirement that RI also be O for mode O prevents the reception of new data until the program has dealt with the old data and reset RI.

Reception can begin in modes I , 2, and 3 if RI is set when the serial stream of bits begins. RI must have been reset by the program before the lasr bit is received or the incoming data will be lost. Incoming data is not transferred to SBUF until the last data bit has been received so that the previous transmission can be read from SBUF while new data is being received. Serial Data Transmission Modes The 1 designers have included four modes of serial data transmission that enable data communication to be done in a variety of ways and a multitude of baud rates.

Pin TXD is connected to the internal shift frequency pulse source to supply shift pulses to external circuits. When transmitting, data is shifted out of RXD, the data changes on the falling edge of S6P2, or one clock pulse after the rising edge of the output TXD shift clock. The sys- tem designer must design the external circuitry that receives this transmitted data to re- ceive the data reliably based on this timing.

External Data Bits Shifted In. Mode 0 is intended not for data communication between computers, but as a high- speed serial data-collection method using discrete logic to achieve high data rates.

The baud rate used in mode 0 will be much higher than standard for any reasonable oscillator frequency; for a 6 megahertz crystal, the shift rate will be kilohertz. Interrupt flag TI is set once all ten bits have been sent. Each bit interval is the inverse of the baud rate frequency, and each bit is maintained high or low over that interval.

Received data is obtained in the same order; reception is triggered by the falling edge of the start bit and continues if the stop bit is true 0 level halfway through the start bit interval. This is an anti-noise measure; if the reception circuit is triggered by noise on the transmission line, the check for a low after half a bit interval should limit false data reception. Data bits are shifted into the receiver at the programmed baud rate, and the data word will be loaded to SBUF ifthe following conditions are true: RI must be 0, and mode bit SM2 is 0 or the stop bit is I the normal state of stop bits.

RI set to 0 implies that the program has read the previous data byte and is ready to receive the next; a normal stop bit will then complete the transfer of data to SBUF regardless of the state of SM2. SM2 set to 0 enables the reception of a byte with any stop bit state, a condition which is of limited use in this mode. SM2 set to I forces reception of only "good" stop bits, an anti-noise safeguard. RI is set to 1, indicating a new data byte has been received.

If RI is found to be set at the end of the reception, indicating that the previously received data byte has not been read by the program, or if the other conditions listed are not true.

Mode 1 Baud Rates Timer I is used to generate the baud rate for mode I by using the overtlow flag of the timer to determine the baud frequency. Typically, timer I is used in timer mode 2 as an autoload 8-hit timer that generates the baud frequency: The oscillator frequency is chosen to help generate both standard and nonstandard b a d rates. If standard baud rates are desired, then an To get a standard rate of hertz then, the setting of THI may be found as follows: Both the start and stop bits are discarded.

The baud rate is programmed as follows: Here, as in the case for mode 0, the baud rate is much higher than standard communica- tion rates.

This high data rate is needed in many multi-processor applications. Data can be collected quickly from an extensive network of communicating microcontrollers if high baud rates are employed.

The conditions for setting RI for mode 2 are similar to mode I: RI must be 0 before the last bit is received, and SM2 must be 0 or the ninth data bit must be a I. Setting RI based upon the state of SM2 in the receiving and the state of bit 9 in the transmitted message makes multiprocessing possible by enabling some receivers to be interrupted by certain messages, while other receivers ignore those messages.

Only those 's that have SM2 set to 0 will be interrupted by received data which has the ninth data bit set too; those with SM2 set to I will not be interrupted by messages with data bit 9 at 0.

All re- ceivers will be interrupted by data words that have the ninth data bit set to I; the state of SM2 will not block reception of such messages.

This scheme allows the transmitting computer to "talk" to selected receiving comput- ers without interrupting other receiving computers. Receiving computers can be com- manded by the "talker" to "listen" or "deafen" by transmitting coded byte s with the ninth data bit set to 1.

The I in data bit 9 interrupts all receivers, instructing those that are programmed to respond to the coded byte s to program the state of SM2 in their respec- tive SCON registers.

Selected listeners then respond to the bit 9 set to 0 messages, while all other receivers ignore these messages. The talker can change the mix of listeners by transmitting bit 9 set to I messages that instruct new listeners to set SM2 to 0,while others are instructed to set SM2 to 1.

Serial Data Mode 3 Mode 3 is identical to mode 2 except that the baud rate is determined exactly as in mode 1, using Timer I to generate communication frequencies. Interrupts A computer program has only two ways to determine the conditions that exist in internal and external circuits.

One method uses software instructions that jump on the states of flags and port pins. The second responds to hardware signals, called interrupts, that force the program to call a sub-routine.

Software techniques use up processor time that could be devoted to other tasks; interrupts take processor time only when action by the program is needed. Set to 1 by program to enable timer 1 overflow interrupt; cleared to 0 to disable timer 1 overflow interrupt.

Set to 1 by program to e n a b l e m interrupt; cleared to O to disable interrupt. Set to 1 by program to e n a b l e m interrupt; cleared to 0 to disable interrupt. Interrupts may be generated by internal chip operations or provided by external sources. Any interrupt can cause the to perform a hardware call to an interrupt- handling subroutine that is located at a predetermined by the designers absolute address in program memory.

Five interrupts are provided in the Three of these are generated automatically by internal operations: Two interrupts are triggered by external signals provided by circuitry that is connected to pins rn and port pins P3.

All interrupt functions are under the control of the program. The programmer is able to alter control bits in the interrupt enable register IE , the intempt priority register lP , and the timer control register TCON. The program can block all or any combination of the interrupts from acting on the program by suitably setting or clearing bits in these regis- ters.

After the interrupt has been handled by the interrupt subroutine, which is placed by the programmer at the interrupt location in program memory, the interrupted program must resume operation at the instruction where the interrupt took place. The PC address will be restored from the stack after an RETl instruction is executed at the end of the interrupt subroutine. The flag is cleared to 0 when the resulting interrupt generates a program call to the appro- priate timer subroutine in memory.

These are ORed together to provide a single interrupt to the processor: These bits are not cleared when the interrupt-generated program call is made by the processor. The program that handles serial data communication must reset RI or TI to 0 to enable the next data communication operation. External Interrupts Pins and are used by external circuitry. The IEX flags may be set when the m p i n signal r e a c h e s low level, or the flags may be set when a high-to-low transition takes place on the INTX pin.

Flags IEX will be reset when a transition-generated interrupt is accepted by the pro- cessor and the interrupt subroutine is accessed. It is the responsibility of the system de- signer and programmer to reset any level-generated external interrupts when they are serviced by the program. The external circuit musr remove the low level before an RETI is executed.

Failure to remove the low will result in an immediate interrupt after RETI, from the same source. Reset A reset can be considered to be the ultimate interrupt because the program may not block the action of the voltage on the RST pin. This type of interrupt is often called "non- maskable," since no combination of bits in any register can stop, or mask the reset action. Unlike other interrupts, the PC is not stored for later program resumption; a reset is an absolute command to jump to program address OOOOh and commence running from there.

Whenever a high level is applied to the RST pin, the enters a reset condition. After the RST pin is brought low, the internal registers will have the values shown in the following table:. Internal RAM is not changed by a reset; however, the states of the internal RAM when power is first applied to the 1 are random.

Register bank 0 is selected upon reset as all hits in PSW are 0. The IE register holds the program- mable bits that can enable or disable all the interrupts as a group, or if the group is en- abled, each individual interrupt source can be enabled or disabled.

Often, it is desirable to be able to set priorities among competing interrupts that may conceivably occur simultaneously. The IP register bits may be set by the program to assign priorities among the various interrupt sources so that more important interrupts can be serviced first should two or more interrupts occur at the same time.

Bit EA is a master, or "global," bit that can enable or disable all of the interrupts. Bits set to 1 give the accompanying interrupt a high priority while a 0 assigns a low priority. Interrupts with a high priority can interrupt another interrupt with a lower priority: If two interrupts with the same priority occur at the same time, then they have the following ranking: IEO 2.

TFO 3. IEl 4. TFI 5. Interrupt Destinations Each interrupt source causes the program to do a hardware call to one of the dedicated addresses in program memory. It is the responsibility of the programmer to place a routine at the address that will service the interrupt. The interrupt saves the PC of the program, which is running at the time the interrupt is serviced on the stack in internal RAM.

A call is then done to the appropriate memory location. These locations are shown in the following table: A RETI instruction at the end of the routine restores the PC to its place in the inter- rupted program and resets the interrupt logic so that another interrupt can be serviced.

Interrupts that occur but are ignored due to any blocking condition IE bit not set or a higher priority interrupt already in process must persist until they are serviced, or they will be lost. This requirement applies primarily to the level-activated tNTX interrupts. Software Generated Interrupts When any interrupt flag is set to I by any means, an interrupt is generated unless blocked. This means that the program itself can cause interrupts of any kind to be generated simply by setting the desired interrupt flag to I using a program instruction.

Summary The internal hardware configuration of the registers and control circuits have been examined at the functional block diagram level. The 1 may be considered to be a col- lection of RAM, ROM, and addressable registers that have some unique functions. Questions Find the following using the information provided i n Chapter 2.

Size of the internal RAM. Internal ROM size in the Execution time o f a single byte instruction for a 6 megahertz crystal.

The bit data addressing registers and their functions. Registers that can do division. The flags that are stored i n the PSW.

Which register holds the serial data interrupt bits T I and RI. Address of the stack when the is reset. Number of register banks and their addresses. Ports used for external memory access. Address of a subroutine that handles a timer I interrupt. Why a low-address byte latch for external memory is needed.

How an pin can be both an input and output. Which port has no alternate functions. The maximum pulse rate that can be counted on pin TI if the oscillator frequency is 6 megahertz.

Which bits in which registers must be set to give the serial data intempt the highest priority. The baud rate for the serial port in mode 0 for a 6 megahertz crystal. The largest possible time delay for a timer in mode 1 if a 6 megahertz crystal is used. The setting of THl. Find the setting for both values of SMOD. The address of the PCON special-function register. The time it will take a timer in mode I to overflow if initially set to 03AEh with a 6 megahertz crystal.

Which bits in which registen must be set to I to have timer 0 count input pulses on pin TO in timer mode 0. The signal that reads external ROM.

When used in rnultipmcessing, which bit in which register is used by a transmitting to signal receiving 's that an interrupt should be generated. The two conditions under which program opcodes are fetched from external, rather than internal, memory. Which bits in which register s must be set to m a k e r n level activated. The address of the interrupt program for the level-generated interrupt. The bit address of bit 4 of RAM byte 2Ah. Moving Data. Introduction A computer typically spends more time moving data from one location to another than it spends on any other operation.

It is not surprising, therefore, to find that more instructions are provided for moving data than for any other type of operation. Data is stored at a source address and moved actually, the data is copied to a desti- nation address. The ways by which these addresses are specified are called the addressing modes. The mnemonics are written with the destination address named first, fol- lowed by the source address. A detailed study of the operational codes opcodes of the 1 begins in this chapter.

Although there are 28 distinct mnemonics that copy data from a source to a destination, they may be divided into the following three main types: MOV destination, source 2. XCH destination, source The following four addressing modes are used to access data: Immediate addressing mode 2. Direct addressing mode 4. Indirect addressing mode The MOV opcodes involve data transfers within the 1 memory. This memory is divided into the following four distinct physical parts: Internal RAM 2. Internal special-function registers 3.

External RAM 4. Internal and external ROM Finally, the following five types of opcodes are used to move data: MOV 2.

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MOVX 3. MOVC 4. Addressing Modes The way in which the data sources or destination addresses are specified in the mnemonic that moves that data determines the addressing mode.

Figure 3. Immediate Addressing Mode The simplest way to get data to a destination is to make the source of the data part of the opcode. The data source is then immediately available as part of the instruction itself. When the executes an immediate data move. Whatever data is found there is copied to the destination address.

The mnemonic for immediate data is the pound sign. Occasionally, in the rush to meet a deadline, one forgets to use the for immediate data. The resulting opcode is often a legal command that is assembled with no objections by the assembler. This omis- sion guarantees that the rush will continue. Register Addressing Mode Certain register names may be used as part of the opcode mnemonic as sources or destina- tions of data.

Other registers in the may be addressed using the direct addressing mode. Some assemblers can equate many of the direct addresses to the register name as is the case with the assembler discussed in this text so that register names may be used in lieu of register addresses. The following table shows all possible MOV opcodes using immediate and register addressing modes: Source Or Destination.

Data Register Addnssing Modc. Data Dinct Addressing Mode. A data MOV does not alter the contents of the data source address. A ropy of the data is made from the source and moved to the destination address. The contents of the destina- tion address are replaced by the source address contents. The following table shows ex- amples of MOV opcodes with immediate and register addressing modes:. All numbers must start with a decimal number , or the assembler assumes the number is a label.

Register-to-register moves using the register addressing mode occur between registers A and RO to R7. Internal RAM uses addresses from 00 to 7Fh to address each byte. Note the use of a leading O for all numbers that begin with an alphabetic alpha character. The direct addresses of the working registers are as follows: Only one bank of working registers is active at any given time.

Reset also sets S P to07h. This growing stack will overwrite the register banks above bank 0. Be sure to set the SP to a number above those of any working registers the program may use. The programmer may choose any other bank by setting RSO and RSI as desired; this bank change is often done to "save" one bank and choose another when servicing an interrupt or using a subroutine.

The moves made possible using direct, immediate, and register addressing modes are as follows:. The following table shows examples of MOV opcodes using direct, immediate, and register addressing modes:. The SFRs are physically on the chip; all other addresses above 7Fh do not physically exist.

Moving data to a port changes the port latch; moving data from a port gets data from the port plns. Moving data from a direct address to Itself IS not predictable and could lead to errors. Inspection of the opcode reveals exactly what are the addresses of the destination and source. The indirect addressing mode uses a register to hold the actual address that will finally be used in the data move; the register itself is not the address, but rather the number in the register.

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The number that is in the pointing register Rp cannot be known un- less the history of the register is known. The mnemonic symbol used for indirect address- ing is the "at" sign, which is printed as. The moves made possible using immediate, direct, register and indirect addressing modes are as follows:. The following table shows examples of MOV opcodes, using immediate, register, direct.

Only registers RO or R 1 may be used for indirect addressing. Opcodes that access this external memory always use indirect addressing to specify the external memory. An X is added to the MOV mnemonics to serve as a reminder that the data move is external to the , as shown in the following table. The following table shows examples of external moves using register and indirect addressing modes:. The data is usually of a temporary or "scratch pad" nature and disap- pears when the system is powered down.

There are times when access to a preprogrammed mass of data is needed, such as when using tables of predefined bytes. This data must be permanent to be of repeated use and is stored in the program ROM using assembler directives that store programmed data anywhere in ROM that the programmer wishes. Access to this data is made possible by using indirect addressing and the A register in conjunction with either the PC or the DFTR, as shown in Figure 3.

In both cases, the number in register A is added to the pointing register to form the address in ROM where the desired data is to be found. The data is then fetched from the ROM address so formed and placed in the A register. The original data in A is lost, and the addressed data takes its place. As shown in the following table, the letter C is added to the MOV mnemonic to high- light the use of the opcodes for moving data from the source address in the Code ROM to the A register in the The following table shows examples of code ROM moves using register and indirect addressing modes:.

All data is moved from the code memory to the A register. The data moves between an area of internal RAM, known as the stack, and the specified direct address. The SP register actually is used in the indirect addressing mode but is nor named in the mnemonic.

A PUSH opcode copies data from the source address to the stack. SP is incremented by one before the data is copied to the internal R A M location contained in SP so that the data is stored from low addresses to high addresses in the internal RAM. The stack grows up in memory as it is PUSHed. A POP opcode copies data from the stack to the destination address. SP is decre- menred by one afler data is copied from the stack R A M addresJto the direct destination to ensure that data placed on the stack is retrieved in the same order as it was stored.

The SP register is set to 07h when the is reset, which is the same direct address in internal RAM as register R7 in bank 0. The SP should be initialized by the programmer to point to an internal RAM address above the highest address likely to be used by the program.

Mnemonic Operation MOV 81h. The SP is usually set at addresses above the reglster banks. Note that direct addresses, not register names, must be used for most registers. The stack mnemonics have no way of knowing which bank is in use. Exchange instmc- tions actually move data in two directions: All addressing modes except immediate may be used in the XCH exchange opcodes:.

Exchanges between A and any port location copy the data on the port pins to A, while the data in A is copied to the port larch. The following table shows examples of data moves using exchange opcodes:. This section concludes the listing of the various data moving instructions; the remain- ing sections will concentrate on using these opcodes to write short programs. Example Programs Programming is at once a skill and an art. Just as anyone may learn to play a musical instmment after sufficient instruction and practice, so may anyone learn to program a computer.

Some individuals, however, have a gift for programming that sets them apart from their peers with the same level of experience, just as some musicians are more tal- ented than their contemporaries. Gifted or not, you will not become adept at programming until you have written and rewritten many programs.

The emphasis here is on practice; you can read many books on how to ride a bicycle, but you do not know how to ride until you do it. If some of the examples and problems seem trivial or without any "real-world" appli- cation, remember the playing of scales on a piano by a budding musician. Each example will be done using several methods; the best method depends upon what resource is in short supply.

If programming time is valuable, then the best program is the one that uses the fewest lines of code; if either ROM or execution time is limited, then the program that uses the fewest code bytes is best. Method 1: Use an immediate number and register addressing. A Copy A to R7 Totals: Use the immediate number to a direct address: Using the immediate number in each instruction uses bytes; use a register to hold the numher: A MOV 34h.

A Totals: There must be a way to avoid naming each address; the PUSH opcode can increment to each address: COMMENT lndtrect addresstng with the number in A and the indirect address in R1 could be done; how- ever, R 1 would have to be loaded with each address from 30h to 34h.

Loading R 1 would take a total of 1 7 bytes and 1 1 lines of code. Summary The opcodes that move data between locations within the and between the and external memory have been discussed. The general form and results of these instructions are as follows.

Enter pincode. Usually delivered in days? Kenneth Ayala. English Binding: Paperback Publisher: Cengage ISBN: Gracias18 2. Frequently Bought Together. The Microcontroller. A Textbook of Railway Engineering. Add 3 Items to Cart. Rate Product. Ujagar Chari Certified downloader , Usgao 11 months ago. Have doubts regarding this product?

Post your question. Safe and Secure Payments. Easy returns.AC, and OV flags are arithmetic flags. This chapter provides a broad overview of the architecture of the 1. Focuses on programming the Intel microcontroller, one of the most common microprocessors used in controls or instrumentation applications using assembly code.

It is important to note that many of the. Engineering Books. This is not true for mode 3; the timers do not operate indepen- dently if mode 3 is chosen for timer 0.

The stack grows up in memory as it is PUSHed. Keep in mind that all such operations are done using each individual bit of the desti- nation and source bytes.