pic16f690-examples
The PIC16F690 is an 8-bit microcontroller from Microchip. Here are some examples:
- System clock - configure the clock
- GPIO - toggle GPIO pins
- Timer with interrupt - configure a timer to interrupt the processor
PIC16F631/677/685/687/689/690 datasheet
Install tools
We'll use sdcc to compile code and pk2cmd to load it into flash program memory.
Build SDCC from source since Debian does not package a version of SDCC that supports pic14 and pic16 ports because of license requirements by Microchip.
sudo apt-get install bison flex libboost-dev g++ gputils texinfo zlib1g-dev automake autoconf-archive libtool
svn checkout https://svn.code.sf.net/p/sdcc/code/trunk sdcc-code
cd sdcc-code/sdcc
./configure
make -j
sudo make install
Build pk2cmd from source since there is no Debian package.
sudo apt-get install libusb-dev
wget http://ww1.microchip.com/downloads/en/DeviceDoc/pk2cmdv1.20LinuxMacSource.tar.gz
extract pk2cmdv1.20LinuxMacSource.tar.gz
cd pk2cmdv1.20LinuxMacSource
make linux
sudo make install
sudo cp /usr/share/pk2/PK2DeviceFile.dat /usr/local/bin
Run a program
Wire up the PICkit 2 to the PIC16F690.
Note: a decoupling capacitor should be placed between Vdd and Vss.
Write a program (empty.c) in C:
#include <pic16f690.h>
void main(void)
{
// Does nothing!
}Compile and run it!
$ sdcc -mpic14 -p16f690 --stack-size 8 --use-non-free empty.c
message: Using default linker script "/usr/share/gputils/lkr/16f690_g.lkr".
$ pk2cmd -PPIC16f690 -Fempty.hex -M -A5.0 -T
PICkit 2 Program Report
26-11-2019, 19:49:07
Device Type: PIC16F690
Program Succeeded.
Operation Succeeded
Note: --stack-size 8 is used because the PIC16F690 can store 8 addresses in its stack:
System clock
Let's use the internal oscillator at 8 MHz and output it on the CLKOUT pin (system-clock-intosc.c):
#include <pic16f690.h>
#include <stdint.h>
static __code uint16_t __at(_CONFIG) config =
_INTOSC & _WDTE_OFF & _PWRTE_OFF & _MCLRE_OFF &
_CP_OFF & _BOR_OFF & _IESO_OFF & _FCMEN_OFF;
void main(void)
{
IRCF2 = 1; IRCF1 = 1; IRCF0 = 1; // Fosc = 8 MHz
SCS = 1;
}FOSC<2:0> of the configuration word register is set to internal oscillator with CLKOUT (_INTOSC). The 8 MHz high frequency oscillator is configured via IRCF<2:0> of the OSCCON register. And, then the internal oscillator is configured by setting the SCS bit of the OSCCON register.
Note: take a couple minutes to read pic16f690.h. It can be found here /usr/local/share/sdcc/non-free/include/pic14/pic16f690.h.
Investigate: The datasheet is somewhat inconsistent about the difference between FOSC<2:0> and SCS. SCS appears to control the MUX that selects between external and internal oscillator, despite its definition, while functionality such as CLKOUT as configured in FOSC<2:0> still takes effect.
If we probe CLKOUT, we'll see a 2 MHz square wave since CLKOUT is defined to be Fosc/4:
How long does it take to switch to 8 MHz?
Holy smokes! 380 us from power up!
GPIO
The PIC16F690 has general purpose I/O pins which are grouped into three ports. TRISA, TRISB, and TRISC can be configured to specify whether a pin is input or output, and PORTA, PORTB, PORTC can be read to get the value of an input pin or written to set the value of an output pin.
Note: When using PORTA pins, ANSEL and ANSELH must be set to 0 to configure the pins as digital I/O. If the pin is configured as analog input, the digital I/O circuitry is disabled.
How fast can we toggle a GPIO pin?
#include <pic16f690.h>
#include <stdint.h>
static __code uint16_t __at(_CONFIG) configword1 =
_INTOSC & _WDTE_OFF & _PWRTE_OFF & _MCLRE_OFF &
_CP_OFF & _BOR_OFF & _IESO_OFF & _FCMEN_OFF;
void main(void)
{
IRCF2 = 1; IRCF1 = 1; IRCF0 = 1; // Fosc = 8 MHz
SCS = 1;
// Disable analog input mode
ANSEL = 0x00;
ANSELH = 0x00;
// Configure PORT I/O pins as output
TRISA = 0x00;
TRISC = 0x00;
TRISB = 0x00;
PORTA = 0x00;
PORTB = 0x00;
PORTC = 0x00;
for (;;) {
RC2 = 1;
RC2 = 0;
}
}
One loop iteration takes 6 instructions. Let's check the assembly (gpio1.asm):
_00106_DS_:
; .line 27; "gpio1.c" RC2 = 1;
BANKSEL _PORTCbits
BSF _PORTCbits,2
; .line 28; "gpio1.c" RC2 = 0;
BCF _PORTCbits,2
GOTO _00106_DS_If we look at section 2.2 Data Memory Organization of the PIC16F690 datasheet, we see that data memory is partitioned into four banks. The bank is selected by configuring RP<1:0> of the STATUS register. For example, to modify the OSCCON register, we must switch to Bank 1 first, and then write to address 0x8F.
BANKSEL is not an instruction, but an assembler directive. To see the complete disassembly, see the list file (gpio1.lst):
_00106_DS_:
; .line 27; "gpio1.c" RC2 = 1;
0000e7 1283 bcf 0x03, 0x5 BANKSEL _PORTCbits
0000e8 1303 bcf 0x03, 0x6
0000e9 1507 bsf 0x07, 0x2 BSF _PORTCbits,2
; .line 28; "gpio1.c" RC2 = 0;
0000ea 1107 bcf 0x07, 0x2 BCF _PORTCbits,2
0000eb 28e7 goto 0x00e7 GOTO _00106_DS_Here we see that BANKSEL clears both RP bits in the STATUS register, which selects Bank 0. Notice the STATUS register is always at address 0x3 in each bank.
So... we don't need to switch banks every time the loop body executes... let's rewrite the loop in assembly gpio2.c:
__asm
banksel PORTC
loop:
bsf PORTC, 2
bcf PORTC, 2
goto loop
__endasm ;
}Now we should expect the body of the loop to take 4 cycles since BSF and BCF take 1 cycle each and GOTO takes 2 cycles:
With a couple extra NOPs we can get a 50% duty cycle square wave. However, it has a jitter of ~10ns and is ~1.1kHz faster than expected:
Timer with interrupt
Timer0 is an 8-bit counter that can be configured to increment according to either an internal or external clock source. When the timer overflows from 0xFF to 0x00, an interrupt will be generated.
Example timer-interrupt.c:
#include <pic16f690.h>
#include <stdint.h>
static __code uint16_t __at(_CONFIG) configword1 =
_INTOSC & _WDTE_OFF & _PWRTE_OFF & _MCLRE_OFF &
_CP_OFF & _BOR_OFF & _IESO_OFF & _FCMEN_OFF;
void isr(void) __interrupt(0)
{
T0IF = 0; // Clear timer interrupt flag.
RC2 = 0;
RC2 = 1; // Set RC2 high for one cycle.
RC2 = 0;
}
void main(void)
{
IRCF2 = 1; IRCF1 = 1; IRCF0 = 1; // Fosc = 8 MHz
SCS = 1;
TRISC = 0x00; // Configure PORTC pins as digital output.
PORTC = 0x00; // Output logic zero on PORTC pins.
T0CS = 0; // Use the internal instruction cycle clock (Fosc/4) as TMR0 clock source.
PSA = 1; // Assign the prescaler to the WDT so that it doesn't affect TMR0.
INTCON = 0; // Disable all interrupt enables and flags.
GIE = 1; // Global interrupt enable.
T0IE = 1; // Enable Timer0 interrupt.
TMR0 = 0; // Reset counter to 0.
for (;;) {
// Do nothing!
}
}
From the list file we see the interrupt service routine located at address 0x4 in program memory with quite a few instructions for saving/restoring a some special function registers:
; .line 8; "timer-interrupt.c" void isr(void) __interrupt(0)
000004 00f2 movwf 0x72 MOVWF WSAVE
000005 0e03 swapf 0x03, 0x0 SWAPF STATUS,W
000006 0183 clrf 0x03 CLRF STATUS
000007 00f1 movwf 0x71 MOVWF SSAVE
000008 080a movf 0x0a, 0x0 MOVF PCLATH,W
000009 018a clrf 0x0a CLRF PCLATH
00000a 00f0 movwf 0x70 MOVWF PSAVE
00000b 0804 movf 0x04, 0x0 MOVF FSR,W
00000c 1283 bcf 0x03, 0x5 BANKSEL ___sdcc_saved_fsr
00000d 1303 bcf 0x03, 0x6
00000e 00ac movwf 0x2c MOVWF ___sdcc_saved_fsr
; .line 10; "timer-interrupt.c" T0IF = 0; // Clear timer interrupt flag.
00000f 1283 bcf 0x03, 0x5 BANKSEL _INTCONbits
000010 1303 bcf 0x03, 0x6
000011 110b bcf 0x0b, 0x2 BCF _INTCONbits,2
; .line 12; "timer-interrupt.c" RC2 = 0;
000012 1107 bcf 0x07, 0x2 BCF _PORTCbits,2
; .line 13; "timer-interrupt.c" RC2 = 1; // Set RC2 high for one cycle.
000013 1507 bsf 0x07, 0x2 BSF _PORTCbits,2
; .line 14; "timer-interrupt.c" RC2 = 0;
000014 1107 bcf 0x07, 0x2 BCF _PORTCbits,2
; .line 15; "timer-interrupt.c" }
000015 1283 bcf 0x03, 0x5 BANKSEL ___sdcc_saved_fsr
000016 1303 bcf 0x03, 0x6
000017 082c movf 0x2c, 0x0 MOVF ___sdcc_saved_fsr,W
000018 1283 bcf 0x03, 0x5 BANKSEL FSR
000019 1303 bcf 0x03, 0x6
00001a 0084 movwf 0x04 MOVWF FSR
00001b 0870 movf 0x70, 0x0 MOVF PSAVE,W
00001c 008a movwf 0x0a MOVWF PCLATH
00001d 0183 clrf 0x03 CLRF STATUS
00001e 0e71 swapf 0x71, 0x0 SWAPF SSAVE,W
00001f 0083 movwf 0x03 MOVWF STATUS
000020 0ef2 swapf 0x72, 0x1 SWAPF WSAVE,F
000021 0e72 swapf 0x72, 0x0 SWAPF WSAVE,W
END_OF_INTERRUPT:
000022 0009 retfie RETFIE