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Programming 8-bit PIC Microcontrollers in C Martin Bates Elsevier 2008
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This presentation contains illustrations from the book
‘Programming 8-bit PIC Microcontrollers in C’ Part 1 Microcontroller Systems describes in detail the internal architecture and interfaces available in the PIC 16F887A, a typical PIC chip, as well as outlining the main features of the development system Part 2 C Programming Essentials provides simple example programs for the microcontroller which show the basic principles of C programming, and interfacing to basic I/O devices Part 3 C Peripheral Interfaces provides example programs for operating PIC chips with a full range of peripherals, using timers and interrupts
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MICROCONTROLLER SYSTEMS
Part 1 MICROCONTROLLER SYSTEMS
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Figure 1.1 Elements of a digital controller
CPU Central Processing Unit Input Peripherals Output ROM Read Only Memory RAM Read & Write Program download User input User output The microcontroller contains all these elements in one chip
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Figure F877 pin-out The microcontroller pins have multiple functions
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Arithmetic & Logic Unit
Figure 1.3 PIC 16F877 MCU Block diagram Flash ROM Program Memory 8192 x 14 bits 0000 – 1FFF Instruction Register MCU control lines Program Counter (13 bits) Stack 13 bits x 8 levels RAM File Registers 368 X 8 bits 000-1FF Data Bus (8 bits) File Select Register Working (W) File Address Literal Op-code Instructions Address Arithmetic & Logic Unit Ports, Timers ADC, Serial I/O Status bits Timing control EEPROM 256 bytes Clock Reset Port A B C D E Program address Instruction Decode & CPU control Status (Flag) Shows the main parts of the chip in simplified form
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Table 1.1 PIC16F877 simplified file register map
Table 1.1 PIC16F877 simplified file register map Bank 0 (000 – 07F) Bank 1 (080 – 0FF) Bank 2 ( ) Bank 3(180-1FF) Address Register 000h Indirect 080h 100h 180h 001h Timer0 081h Option 101h 181h 002h PC Low 082h 102h 182h 003h Status Reg 083h 103h 183h 004h File Select 084h 104h 184h 005h Port A data 085h PortA direction 105h - 185h 006h Port B data 086h PortB direction 106h 186h 007h Port C data 087h PortC direction 107h 187h 008h Port D data 088h PortD direction 108h 188h 009h Port E data 089h PortE direction 109h 189h 00Ah PC High 08Ah 10Ah 18Ah 00Bh Interrupt Control 08Bh 10Bh 18Bh 00Ch to 01Fh 20 Peripheral Control Registers 08Ch 09Fh 10Ch 10Fh 4 Peripheral 18Ch 18Fh 110h 16Fh 96 General Purpose 190h 1EFh 96 General 020h 06Fh 80 General 0A0h 0EFh 070h 07Fh 16 Common Access GPRs 0F0h 0FFh Accesses 70h – 7Fh 170h 17Fh Accesses 1F0h 1FFh
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Table 1.2 PIC microcontroller types
MCU Pins Data word (bits) Program memory (bytes) Typical Instruction Set Speed MIPS Comment 10FXXX = 6 8 <= 512 33 x 12 bits <= 2 Low pin count, small form factor, cheap No EEPROM, none low power, assembler program 12FXXX = 8 <= 2 KB 12 / 14 bits <= 5 EEPROM, 10-bit ADC, some low power, assembler 16FXXX <= 64 <= 14 KB 35 x 14 bits Mid-range, UART, I2C, SPI many low power, C or assembler program 18FXXXX <= 100 <= 128 KB 75 x 16 bits <= 16 High range, CAN, USB J series 3V supply, C program 24FXXXX 16 76 x 24 bits = 16 Power range, 3V supply, no EEPROM, data RAM < 8 KB, C program
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Figure 1.4 I/O pin operation
CPU Data Bus Output Current Driver Data Latch Direction Tri-state Enable Input Write data bit Read data bit Write TRIS bit Analogue input multiplexer The pin can be set for input or output data transfer
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Figure 1.5 General Timer Operation
Binary Counter Pre-scaler (clock divide) Post-scaler (output divide) Timer Overflow/ Timeout (Interrupt) Flag Clock Source Select Instruction Clock External Pulse Capture register Compare register Capture signal Match flag A binary counter is used as a timer when driven from the clock
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The ADC converts an analog input into a binary code
Figure 1.6 ADC operation ANx Analogue to Digital Converter Vref+ Input volts 0-Vf Reference volts, Vf 8-bit or 16-bit integer result Setup ADC Read ADC The ADC converts an analog input into a binary code
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Figure 1.7 Comparator operation
Vc+ Vc- Compartor status bit Vc+ > Vc- The comparator simply sets a bit if one input is higher than the other
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Figure 1.8 Parallel Slave Port operation
Chip select Read Write EXTERNAL Data x 8 Interrupt INTERNAL The PSP allows an external data bus to be connected to the MCU
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Table 1.3 Interrupts sources in the PIC 16F877
Interrupt Source Interrupt trigger event CCS C Interrupt label TIMERS Timer 0 Timer 0 register overflow INT_TIMER0 Timer 1 Timer 1 register overflow INT_TIMER1 CCP 1 Timer 1 capture or compare detected INT_CCP1 Timer 2 Timer 2 register overflow INT_TIMER2 CCP2 Timer 2 capture or compare detected INT_CCP2 PORTS RB0/INT pin Change on single pin RB0 INT_EXT Port B pins Change on any of four pins RB4 – RB7 INT_RB Parallel Slave Port Data received at PSP (write input active) INT_PSP Analog Converter A/D conversion completed INT_AD Analog Comparator Voltage compare true INT_COMP SERIAL UART Serial Port Received data available INT_RDA Transmit data buffer empty INT_TBE SPI Serial Port Data transfer completed (read or write) INT_SSP I2C Serial Port Interface activity detected Bus collision detected INT_BUSCOL MEMORY EEPROM Non-volatile data memory write complete INT_EEPROM
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Figure 1.9 Timer Interrupt Process
Program Execution 1 Start counter statement 2 Run Counter until overflow 5 Time-out Process (Interrupt Service Routine) 7 Continue 3 Timeout Interrupt 6 Return from 4 Jump to ISR Time-out forces the program to be suspended and the ISR executed
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Line drivers convert the signal to a bipolar, higher voltage
Figure 1.10 USART RS232 Signal PIC MCU TX1 Transmit RX1 Receive Ground HOST PC RX2 TX2 COM PORT Line Driver Interface +/- 12V Line drivers convert the signal to a bipolar, higher voltage
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Figure 1.11 Typical USART RS232 signal
Bit 2 3 Idle Start 1 4 5 6 7 Stop Time Bit period The data bits are timed from the falling edge of the start bit
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Figure 1.12 SPI Connections
Master Serial Data Out, SDO Serial Data In, SDI Serial Clock, SCK Slave Select SS1 Outputs SS2 SS3 Slave 1 SDO SDI SCK !SS Slave 2 SPI uses hardware slave selection and separate clock
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Each data bit is transferred on the falling edge of the clock
Figure 1.13 SPI Signals SDO/SDI Data bits SCK Clock Each data bit is transferred on the falling edge of the clock
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Slave selection uses addresses issued by the Master
Figure 1.14 I2C Connections +5V Master Slave1 Slave2 etc SDA SCL Slave selection uses addresses issued by the Master
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Data is strobed in using the master clock, and reception
Figure 1.15 I2C Signals Start Acknowledge Address / Data bits SDA SCL Data is strobed in using the master clock, and reception is acknowledged by the slave by taking the data line low
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Listing 1.1 A simple C program
/* OUTBYTE.C MPB V1.0 */ #include "16F877A.h" // MCU select void main() // Main block { output_D(255); // Switch on outputs } This minimal program outputs a binary code to Port D
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Listing 1.2 Program hex file
: A F : F149F141F159F C : FF :02400E00733FFE : FF ;PIC16F877A The machine code is downloaded as a binary file to the chip
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Figure 1.16 Screenshot of MPLAB Project
The C program is compiled and tested in simulation mode
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Figure 1.17 PICkit2 demo system hardware
Basic hardware for downloading the program to a test board
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Figure 1.18 ICSP target board connections
Application Board MCU Vpp/!MCLR Vdd Vss PGD PGC 1 2 3 4 5 ICSP Interface Reset 10k Vdd Vss Board +5V Supply Connections to the target chip for programming
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Figure 1.19 PICkit2 programmer dialogue
On-screen window for program downloading to target chip
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Figure 1.20 Microchip ICD2 module
ICD2 provides in-circuit debugging
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Figure 1.21 ICD2 program and debug system
Host PC MPLAB development system + C Compiler ICD2 interface PIC MCU Target System USB 6-WAY connector Block diagram of the ICD2 programming and in-circuit debugging system
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Figure 1.22 ICD debugging windows
User interface for in-circuit programming & debugging
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