MICROPROCESSORS & MICROCONTROLLERS
- 2. Microprocessors & Microcontrollers KAFAZ- 1 Version 2021 Khalil Zeineddine P I C 1 6 F 8 7 7 A Chapter _1: To know: 1. Introduction to PIC16F877a 2. Pin out of PIC 3. Internal architecture of PIC 4. Basic elements of PIC Contents_1: PIC Introduction Peripheral Interface Controllers (PIC) is one of the advanced microcontrollers developed by microchip technologies. These microcontrollers are widely used in modern electronics applications. A PIC controller integrates all type of advanced interfacing ports and memory modules. These controllers are more advanced than normal microcontroller like 8051. The first PIC chip was announced in 1975 (PIC1650). As like normal microcontroller, the PIC chip also combines a microprocessor unit called CPU and is integrated with various types of memory modules (RAM, ROM, EEPROM ,etc), I/O ports, timers/counters, communication ports, etc. All PIC microcontroller family uses Harvard architecture. This architecture has the program and data accessed from separate memories so the device has a program memory bus and a data memory bus (more than 8 lines in a normal bus). This improves the bandwidth (data throughput) over traditional von Neumann architecture where program and data are fetched from the same memory (accesses over the same bus). Separating program and data memory
- 3. Microprocessors & Microcontrollers KAFAZ- 2 Version 2021 Khalil Zeineddine P I C 1 6 F 8 7 7 A further allows instructions to be sized differently than the 8-bit wide data word. Now we will move to PIC16F877A. Introduction au PIC16F877a The essential elements of the PIC 16F877 are: • A flash EEPROM type program memory of 8K 14-bit words, • A data RAM of 368 bytes, • A 256-byte EEPROM memory, • 05 input output ports, A (6 bits), B (8 bits), C (8 bits), D (8 bits) and E (3 bits) • 10-bit Analog to Digital converter with 8 selectable inputs, • USART, Universal serial port, asynchronous mode and synchronous mode • SSP, Synchronous serial port • Three TIMERS with their Prescaler, TMR0, TMR1, TMR2 • Two comparison modules and Capture CCP1 and CCP2 • 15 interrupt sources, • Clock generator, quartz (up to 20 MHz) • Code protection, • Operating voltage from 2 to 5V, • Sets of 35 instructions.
- 4. Microprocessors & Microcontrollers KAFAZ- 3 Version 2021 Khalil Zeineddine P I C 1 6 F 8 7 7 A Pin out : The PIC 16F877A box described in the figure below includes 40 pins: 1. 33 input / output pins (5 following ports): • Port A: 6 I / O pins numbered from RA0 to RA5 • Port B: 8 I / O pins numbered from RB0 to RB7 • Port C: 8 I / O pins numbered from RC0 to RC7 • Port D: 8 I / O pins numbered from RD0 to RD7 • Port E: 3 I / O pins numbered from RE0 to RE2 Max output current: 20mA / pin; 200mA / port
- 5. Microprocessors & Microcontrollers KAFAZ- 4 Version 2021 Khalil Zeineddine P I C 1 6 F 8 7 7 A 2. The VDD and VSS pins are used to power the PIC. Note that we have 2 "VDD" connections and 2 "VSS" connections. 3. The pins OSC1 and OSC2 or CLKIN and CLOUT are used to operate the internal oscillator of the PIC. 4. The MCLR pin is used to initialize the MC in the event of power-up, external reset, watchdog and in the event of supply voltage drop. Internal Architecture 1. The CPU executes the program instructions (encoded in 14 bits), processes and generates operations on digital information. 2. The 368 byte Random Access Memory (RAM) is used for temporary storage of data and results. 3. The 256-byte read-only memory (EEPROM) keeps valuable data semi-permanently. 4. The 8k x 14bits FLASH memory is used to store the program (instructions). 5. The clock generates the signal that rates the execution of instructions. 6. Bidirectional ports (A - E) allow communication with the outside; the lines of each port can be programmed as input or output. 7. The timers (3), programmable modules whose functions are: • Astable (periodic signals) • Monostable (impulse) • Counter • PWM signals (direct current motor control). 8. The 10-bit analog / digital converter ADC - 8 inputs available from 0 to 5V; the results of the conversions are stored in internal registers.
- 6. Microprocessors & Microcontrollers KAFAZ- 5 Version 2021 Khalil Zeineddine P I C 1 6 F 8 7 7 A The basic elements of the PIC 16F877A 1. The clock The clock can be either internal or external. The internal clock consists of a crystal oscillator or an RC oscillator. With the Quartz oscillator, we can have frequencies up to 20 MHz depending on the type of μC. 2. The ALU and the W accumulator The ALU is an 8-Bit Arithmetic and Logic Unit which performs basic arithmetic and logic operations. Accumulator W is an 8-bit working register, all two-operand operations go through it. Can we have : An instruction on a single operand which is usually a register located in RAM. An instruction on 2 operands. In this case, one of the two operands is always the accumulator W, the other can be either a register or a constant. 3. RAM memory The addressable RAM memory space is 512 positions of 1 byte each:
- 7. Microprocessors & Microcontrollers KAFAZ- 6 Version 2021 Khalil Zeineddine P I C 1 6 F 8 7 7 A 96 positions are reserved for the SFR (Special Function Registers) which are the PIC configuration registers. The remaining 416 positions constitute the GPR registers (General Propose Registers) or user RAM. On the 16F877, 3 blocks of 16 bytes each are not physically implanted resulting in a user RAM capacity of 368 GPR. 4. Permanent memories The PIC 16F877 has 2 permanent memories. PROGRAM EEPROM memory with a capacity of 8k 14-bit words. The DATA EEPROM memory with a capacity of 256 bytes.