Feature RAM (bytes) Times I/O Pins Serial port Interrupts sources 6 8 6

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1 Topic 1 (16 M) 8051 Microcontroller 1.1 Introduction to 8051 family Microcontroller Microcontroller 1. Salient Features 2. Pins description 3. Architecture of Special function Register (SFR) 5. Memory organization 6. I/O ports, Timer/counters, Interrupt structure 7. Serial port interface 8. Boolean operation 9. Power Down Operation 1.1 Introduction to 8051 family Microcontroller Now a days we seen the introduction of a technology that has radically changed the way in which we control the world around us. We see the many components are use a microcontrollers. Microcontroller is a computer on chip. We see the smart DVD, Video games, TV, Automobiles, home security, microwaves, AC, etc. There are two other members in the 8051 family microcontroller, they are Comparison of 8051 family members Feature ROM (on chip program space in 4 K 8 K 0 K bytes) RAM (bytes) Times I/O Pins Serial port Interrupts sources The 8051 is the most popular member of the 8051 family, this is because the 8051 is available in different memory types, such as UV-EPROM, flash, NV-RAM. Some Companies producing 8051 family 1. Intel 2. Atmel 3. Philips 4. Siemens 5. Dallas Semiconductor

2 Different in Microprocessor and Microcontroller Microprocessor Microprocessor is heart of Computer system. Microprocessor externally connect ROM, RAM, I/O ports, and Timer. Since memory and I/O has to be connected externally, the circuit becomes large. Cannot be used in compact systems and hence inefficient Cost of the entire system increases Due to external components, the entire power consumption is high. Hence it is not suitable to use with devices running on stored power like batteries. Most of the microprocessors do not have power saving features. Since memory and I/O components are all external, each instruction will need external operation, hence it is relatively slower. Microprocessor have less number of registers, hence more operations are memory based. Microprocessors are based on von Neumann model/architecture where program and data are stored in same memory module Mainly used in personal computers Microcontroller Micro Controller is a heart of embedded system. Microcontroller is a single chip available all this ROM, RAM, I/O ports, and Timer. Since memory and I/O are present internally, the circuit is small. Can be used in compact systems and hence it is an efficient technique Cost of the entire system is low Since external components are low, total power consumption is less and can be used with devices running on stored power like batteries. Most of the micro controllers have power saving modes like idle mode and power saving mode. This helps to reduce power consumption even further. Since components are internal, most of the operations are internal instruction, hence speed is fast. Micro controller have more number of registers, hence the programs are easier to write. Micro controllers are based on Harvard architecture where program memory and Data memory are separate Used mainly in washing machine, MP3 players, TV, Automobile, etc. (AT89C51, AT89LV51, AT89C52, DS5000-8, etc.)

3 Microcontroller 1. Salient Features Feature 8051 ROM (on chip program space in 4 K bytes) RAM (bytes) 128 Times 2 I/O Pins 32 Serial port 1 Interrupts sources KB on chip program memory (ROM or EPROM)) bytes on chip data memory (RAM) bit data bus bit address bus general purpose registers each of 8 bits 6. Two -16 bit timers T0 and T1 7. Five Interrupts (3 internal and 2 external). 8. Four Parallel ports each of 8-bits (PORT0, PORT1, PORT2, PORT3) with a total of 32 I/O lines. 9. One 16-bit program counter and One 16-bit DPTR (data pointer) 10. One 8-bit stack pointer 11. One Microsecond instruction cycle with 12 MHz Crystal. 12. One full duplex serial communication port.

4 2. Pins descriptions 8051 microcontroller has available 40 DIP pins. Out of this 32 pins use to I/O Ports as P0, P1, P2, and P3. Pin No. 20 and 40 use to Ground and +5V power. Pin No. 9 use to Reset to 8051 microcontroller for working from starting address. Pin no.29, 30 and 31 use to PSEN, ALE, EA respectively, PSEN use to program store enable, ALE is Address Latch enable and EA use to external enable. Pin no. 1 to 9 use to Port 1 for I/O function.

5 Pin no 10 to 17 use to port 3, working for this port is dual type first is I/O function and second is read, Write, Timer, serial data communication and external interrupt. Pin no. 21 to 28 use to Port 2, working for this port is dual type first is I/O function and second is Address Bus. Pin no. 32 to 39 use to Port 0, working for this port is dual type first is I/O function and second is Address and data bus communication. And last pin no. 18 and 19 use for a crystal oscillator for XTAL 2 and XTAL 1 3. Architecture of 8051

6 The 8051 architecture consists of these specific features Eight bit CPU with register A ( the accumulator ) and B Sixteen bit program counter ( PC ) and Data Pointer ( DPTR ) Eight bit program status world ( PSW ) Eight bit stack pointer ( SP ) Internal ROM or EPROM 4K Internal RAM of 128 bytes 1. Four register banks, each containing eight registers 2. Sixteen bytes, which may be addressed at the bit level 3. Eight bytes of general-purpose data memory Thirty two input/output pins arranged as four 8-bit ports P0 P3 Two 16 bit timer/counters T0 and T1 Full duplex serial data receiver/transmitter SBUF Control registers TCON, TMOD, SCON, PCON, IP, and IE Two external and three internal interrupt sources Oscillator and clock circuits

7 The 8051 oscillator and clock The heart of the 8051 is the circuitry that generate the clock pulses by which all internal operations works. Pin XTAL1 and XTAL2 are provided for connecting a resonant network to form an oscillator. Quartz crystal and capacitors are worked for generating this clock pulses. Crystal frequency is the basic internal clock frequency of the microcontroller design to run 1 megahertz to 16 megahertz. Serial communication needs often dictate the frequency of the oscillator because the requirement that internal counter must divide the basic clock frequency. Program instructions may require one, two, or four machine cycles to be executed, depending on the type of instruction. To calculate the time any particular instruction will take to be executed, find the number of cycles, C. the time to execute that instruction is then found by multiplying c by 12 and dividing the product by the crystal frequency. Tinst=(C*12 d)/crystal frequency

8 Program Counter and Data Pointer The 8051 contains two 16-bit registers 1. Program counter (PC) 2. Data Pointer (DPTR) 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, Program ROM may be on chip at addresses 0000h to 0FFFh, external to exceed 0000h to FFFFh. The PC is automatically incremented after every instruction byte is fetched. The PC is only register that does not have an internal address. The DPTR register is made up of two 8-bit register, named DPH and DPL They are uses for internal and external code access and external data access. DPTR does not have a single internal address. A and B CPU Registers The 8051 contains 34 general purpose or working registers. Two of these registers A and B, hold result of many instructions, particularly math and logical operations, of the 8051 central processing unit (CPU). The other 32 are arranged as part of internal RAM in four banks, B0 B3. The A (accumulator) register is the most versatile of the two CPU registers and is used for many operations, including addition, subtraction, internal multiplication and division. And Boolean bit manipulations. The A register also used for all data transfers between the 8051 and any external memory. The b register 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.

9 Flags and the Program Status World (PSW) Flags are 1-bit registers provided to store the result of certain program instructions. Other instructions can test the condition of the flags and make decisions based on the flag states. The 8051 has four math flags that respond automatically to the outcomes of math operations and three general purpose user flags that can be set to 1 or cleared to 0 by the programmer as designed. The math flags include Carry (C), Auxiliary Carry (AC), Overflow (OV), and Parity (P). User flags are named F0, GF0 and GF1. Internal Memory: - A functioning computer must have memory for program code bytes, commonly in ROM, and RAM memory for variable data that can be altered as the program runs. The 8051 has internal RAM and ROM memory for these functions. Additional memory can be added externally using suitable circuits which use same address in different memories, for code and data. Internal circuitry accesses the correct memory based on the nature of the operation in progress.

10 Internal RAM 8051 has a 128-byte of internal RAM. Thirty two bytes from address 00h to 1Fh that make up 32 working registers organized as four banks of eight registers each. The four register banks are numbered 0 to 3 and are made up of eight registers named R0 to R7. Each register can be addressed by name or by its RAM address. Bit addressable area of 16 bytes occupies RAM byte addresses 20h to 2Fh, forming a total of 128 addressable bits. Addressable bit may be specified by its bit address of 00h to 7Fh, or bits may form any byte address from 20h to 2Fh. A general purpose RAM area above the bit area, from 30h to 7Fh, addressable as bytes. Special Function Register (SFR): - The 8051 operations that do not use the internal 128-byte RAM addresses from 00h to 7Fh are done by a group of specific internal registers, each called a Special Function Register (SFR). Which may be addressed much like internal RAM, using addresses from 80h to FFh. Some SFRs are also bit addressable, as is the case for the bit area of RAM. This feature allows the programmer to change only what needs to be altered, leaving the remaining bits in that SFR unchanged. Not all of the addresses from 80h to FFh are used for SFR, and attempting to use an address that is not defined, or empty, result in unpredictable result. The SFR names and equivalent internal RAM addresses show in table. PC is not a part of the SFR and has no internal RAM address.

11 Internal ROM The 8051 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. Corresponding block of internal program code, contained in an internal Rom, occupies code address space 0000h to 0FFFh. The PC is ordinarily used to address program code bytes from addresses 0000h to 0FFFh. Program addresses higher than 0FFFh, which exceed the internal ROM capacity, will cause the 8051 to automatically fetch code bytes from external program memory. Code bytes can also be fetched exclusively from an external memory, addresses 0000h to FFFFh, by connecting the external access pin (EA pin 31) to ground. Input/output (I/O) ports:- One major feature of a microcontroller is the versatility built into the input / output circuits that connect the 8051 to the outside world. Microcontroller has 32 I/O pins.

12 They have a three ports P0, P1, P2, and P3. Each port has eight pins 0 to 7. Port 0: - Port 0 pins may serve as input as inputs, outputs when used together as a bidirectional low order address and data bus for external memory. Pins used for this port is Pin No. 32 to 39. For example when a pin is to be used as input, a 1 must be written to corresponding port 0 latch be the program, thus turning the output transistors off. Pin latches that are programmed to a 0 will turn on. External pull-up resisters will be needed to supply a login 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. This pins also use to Data bus, so both address and data bus indicating this port is AD0 to AD7. Port 1:- Port 1 pins have no dual functions. Output latch is connected directly to the gate of the lower FET (field effect transistors). Programming logic implemented to this port pins directly. Pins used for this port is Pin No. 1 to 8. Port 2: - Port 2 may be used as an input / output port similar in operation to port 1. The alternate use of 2 is to supply a high order address byte. Port 2 use an address line A8 to A15. Pins used for this port is Pin No. 21 to 28. Port 3: - Port 3 is an input / output port similar to port 1. Pins used for this port is pin no. 10 to 17. Port 3 is alternate use

13 External Memory The system designer is not limited by the amount of internal RAM and ROM available on chip. Two separate external memory spaces are made available by the 16-bit PC and DPTR and by different control pins for enabling external ROM and RAM chips. Internal control circuitry accesses the correct physical memory, depending on the machine cycle state and the opcode being executed. There are several reasons for adding external memory, particularly program memory, when applying the 8051 in a system. Counters and Timers Many microcontroller applications require the counting of external events, such as the frequency of a pulse train, or the generation of precise internal time delays between computer actions. Both of 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. The relieve the processor of this burden, two 16-bit up counters, named T0 and T1, are provided for the general use of the programmer. Each counter may be programmed to count internal clock pulses, acting as a timer, or programmed to count external pulses as a counter. The counter are divided into two 8-bit registers called the timer low (TL0, TL1) and timer high (TH0, TH1) bytes. All counter action is controlled by bit states in the timer mode control register (TMOD), the timer/counter control register (TCON), and certain program instructions.

14 Timer Counter Interrupts The counters have been included on the chip to relieve the processor of timing and counting chores. When program wishes to count a certain number of internal pulses or external events, a number is placed in one of the counters. The number represents the maximum count less the desired count, plus 1. The counter increments from the initial number to the maximum and then rolls over to 0 on the final pulse and also sets a timer flag. Timing If a counter is programmed to be a timer, it will count the internal clock frequency of 8051 oscillator divided by 12d. As example the crystal frequency is 6.0 megahertz, then the timer clock will have a frequency of 500 kilohertz. The resultant timer clock is gated to the timer by means of the circuit show in figure. Figure: - Timer/Counter Control Logic Timer Modes of Operation The timers may operate in any one of four modes that are determined by the mode bits, M1 and M0, in the TMOD register.

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16 Serial Data Input / Output Computers must be able to communicate with other computers in modern multiprocessor distributed system. One cost-effective way to communicate is to send and receive data bits serially. The 8051 has a serial data communication circuit that uses register SBUF to hold data. Register SCON controls data communication, register PCON controls data rates, and pins RXD (P3.0) and TXD (P3.1) connect to the serial data network. Serial Data Interrupts Serial data communication is a relatively slow process, occupying many milliseconds per data byte to accomplish. In order not to tie up valuable processor time, serial data flags are included in SCON to aid in efficient data transmission and reception.

17 Notice that data transmission is under the complete control of the program, but reception of data is unpredictable and at random times that are beyond the control of the program.

18 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 to subroutines on the states of flags and port pins. The second method responds to hardware signals, called interrupts that force the program to call a subroutine. 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. Timer flag interrupt When a timer / counter overflows, the corresponding timer flag, TF0 or TF1, is set to 1.

19 The flag is cleared to 0 when the resulting interrupt generates a program call to the appropriate timer subroutine in memory. Serial Port Interrupt If a data byte is received, an interrupt bit, is set to 1 in the SCON register. When a data byte has been transmitted an interrupt bit, TI, is set in SCON. The program that handles serial data communication must reset RI or TI to 0 to enable the next data communication operation. External Interrupts Pins INT0 and INT1 are used by external circuitry. Inputs on these pins can set the interrupt flags IE0 and IE1 in the TCON register to 1 by two different methods.

20 Assignment 1. Draw the format of PSW. Explain the function of each bit. 2. State the salient features of microcontroller List the alternate function of 8051 port 3 pins. Also write the instruction to set all the port 1 pins as input. 4. Draw and explain the RAM structure of Draw the structure of port 0 of Also state the need of pull up resistors 6. Explain various power saving modes of microcontroller Draw format of TMOD SFR. Explain the function of each bit 8. Draw the format of IE SFR. Explain the function of each bit. Write an instruction to enable only timer interrupt. 9. Explain SFR with diagram. 10. Explain 8051 oscillator and clock. 11. Draw the 8051 Pin out Diagram.