implemented own I2C protocol
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03dfdc0737
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pic/MDR/I2C.c
235
pic/MDR/I2C.c
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@ -1,159 +1,126 @@
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/* software bit banging implementation
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* based on https://en.wikipedia.org/wiki/I2c example code
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*
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* there is no external pull-up on SCL, and the internal one is too weak
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* SCL must be driven
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* but that is ok as we are the only master
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* there is an external pull-up on SDA, and the internal one is too weak
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* SDA goes to 3V instead of 5V due to the external pull-up
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* but the 24LC256 still seems to work
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*/
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#define __16f1847
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#include <pic16f1847.h>
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#include <stdint.h>
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#include "I2C.h"
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// Hardware-specific support functions that MUST be customized:
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/* even when doing nothing, the max speed will be 100kHz, while the chip supports 400kHz */
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#define I2C_delay()
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/* set clock high (default state) */
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#define release_SCL() LATB |= SCL
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/* set clock low */
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#define hold_SCL() LATB &= ~SCL
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/* set data high (default state) */
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#define release_SDA() LATB |= SDA
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/* set data low */
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#define hold_SDA() LATB &= ~SDA
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/* Set SCL as input and return current level of line, 0 or 1 */
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bool read_SCL(void)
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/* a small delay for better clock */
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#define WAIT 1
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/*
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void delay(void)
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{
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LATB |= SCL; /* set high (must be driven because no pull-up */
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return 1;
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uint8_t wait=WAIT;
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while (wait--);
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}
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*/
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#define delay() __asm\
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nop\
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nop\
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nop\
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nop\
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__endasm
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/* read SDA
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* don't forget to set SDA as input in the begining
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* are set SDA as output in the end
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*/
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uint8_t read_SDA(void)
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{
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hold_SCL(); /* set clock to low for SDA to change */
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delay(); /* wait for SDA to change */
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delay();
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delay();
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release_SCL(); /* SDA should be valid when clock is high */
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delay();
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/* we don't verify the SCL state as only we can drive it */
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if (PORTB&SDA) { /* read bit */
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return 1;
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} else {
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return 0;
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}
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}
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/* Set SDA as input and return current level of line, 0 or 1 */
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bool read_SDA(void)
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uint8_t read_ack(void)
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{
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uint8_t ack = 0;
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TRISB |= SDA; /* set as input */
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return (PORTB&SDA)!=0;
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ack = read_SDA();
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TRISB &= ~SDA; /* set back to output */
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hold_SCL();
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return ack;
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}
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/* Actively drive SCL signal low */
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void clear_SCL(void)
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/* start bit is when SDA goes low while SCL is high */
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void send_start(void)
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{
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LATB &= ~SCL; /* set low */
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release_SCL();
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delay();
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release_SDA(); /* ensure SDA is high on the beginning */
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delay();
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hold_SDA();
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}
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/* Actively drive SDA signal low */
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void clear_SDA(void)
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void send_stop(void)
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{
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TRISB &= ~SDA; /* set as output */
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LATB &= ~SDA; /* set low */
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hold_SDA(); /* be sure SDA is low */
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release_SCL();
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delay();
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release_SDA(); /* set SDA high while SCL is high */
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}
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void arbitration_lost(void)
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void send_1(void)
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{
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/* do nothing, since we are the only master */
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hold_SCL(); /* value can change when SCL is low */
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delay();
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release_SDA(); /* set the right state */
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delay();
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release_SCL(); /* value will be read when SCL goes high */
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}
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bool started = false; // global data
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void i2c_start_cond(void) {
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if (started) { // if started, do a restart cond
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// set SDA to 1
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read_SDA();
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I2C_delay();
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while (read_SCL() == 0) { // Clock stretching
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// You should add timeout to this loop
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}
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// Repeated start setup time, minimum 4.7us
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I2C_delay();
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}
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if (read_SDA() == 0) {
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arbitration_lost();
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}
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// SCL is high, set SDA from 1 to 0.
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clear_SDA();
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I2C_delay();
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clear_SCL();
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started = true;
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}
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void i2c_stop_cond(void){
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// set SDA to 0
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clear_SDA();
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I2C_delay();
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// Clock stretching
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while (read_SCL() == 0) {
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// add timeout to this loop.
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}
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// Stop bit setup time, minimum 4us
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I2C_delay();
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// SCL is high, set SDA from 0 to 1
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if (read_SDA() == 0) {
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arbitration_lost();
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}
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I2C_delay();
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started = false;
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}
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// Write a bit to I2C bus
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void i2c_write_bit(bool bit) {
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if (bit) {
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read_SDA();
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} else {
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clear_SDA();
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}
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I2C_delay();
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while (read_SCL() == 0) { // Clock stretching
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// You should add timeout to this loop
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}
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// SCL is high, now data is valid
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// If SDA is high, check that nobody else is driving SDA
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if (bit && read_SDA() == 0) {
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arbitration_lost();
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}
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I2C_delay();
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clear_SCL();
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}
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// Read a bit from I2C bus
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bool i2c_read_bit(void) {
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bool bit;
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// Let the slave drive data
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read_SDA();
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I2C_delay();
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while (read_SCL() == 0) { // Clock stretching
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// You should add timeout to this loop
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}
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// SCL is high, now data is valid
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bit = read_SDA();
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I2C_delay();
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clear_SCL();
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return bit;
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}
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// Write a byte to I2C bus. Return 0 if ack by the slave.
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bool i2c_write_byte(bool send_start, bool send_stop, unsigned char byte)
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void send_0(void)
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{
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unsigned bit;
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bool nack;
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if (send_start) {
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i2c_start_cond();
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}
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hold_SCL(); /* value can change when SCL is low */
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delay();
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hold_SDA(); /* set the right state */
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delay();
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release_SCL(); /* value will be read when SCL goes high */
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}
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/* send byte and get ack */
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uint8_t send_byte(uint8_t byte)
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{
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uint8_t bit;
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/* send every bit, MSb first */
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for (bit = 0; bit < 8; bit++) {
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i2c_write_bit((byte & 0x80) != 0);
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if (byte&0x80) {
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send_1();
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} else {
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send_0();
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}
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byte <<= 1;
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}
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nack = i2c_read_bit();
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if (send_stop) {
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i2c_stop_cond();
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}
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return nack;
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}
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// Read a byte from I2C bus
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unsigned char i2c_read_byte(bool nack, bool send_stop)
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{
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unsigned char byte = 0;
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unsigned bit;
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for (bit = 0; bit < 8; bit++) {
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byte = (byte << 1) | i2c_read_bit();
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}
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i2c_write_bit(nack);
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if (send_stop) {
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i2c_stop_cond();
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}
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return byte;
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return read_ack();
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}
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uint8_t read_byte(void)
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{
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uint8_t byte = 0;
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uint8_t bit;
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TRISB |= SDA; /* set as input */
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/* read 8 bits */
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for (bit=0; bit<8; bit++) {
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byte += read_SDA();
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byte <<= 1;
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}
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TRISB &= ~SDA; /* set back to output */
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send_0(); /* send ack */
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return byte;
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}
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@ -2,15 +2,11 @@
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#include <pic16f1847.h>
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#include <stdint.h>
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#define bool uint8_t
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#define true 1
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#define false 0
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#define SCL _RB6 /* pin 12, external 24LC256 I2C EEPROM memory */
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#define SDA _RB7 /* pin 13, external 24LC256 I2C EEPROM memory */
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// Write a byte to I2C bus. Return 0 if ack by the slave.
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bool i2c_write_byte(bool send_start, bool send_stop, unsigned char byte);
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// Read a byte from I2C bus
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unsigned char i2c_read_byte(bool nack, bool send_stop);
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void send_start(void);
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void send_stop(void);
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uint8_t send_byte(uint8_t byte);
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uint8_t read_byte(void);
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@ -116,8 +116,8 @@ void init (void) {
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* this PIC16F1847 offers hardware I2C, but not on those pins
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* so we also have to use software bit banging I2C
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*/
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TRISB &= ~SCL; /* set as output (it must be driven because there is no pull-up */
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LATB |= SCL; /* set clock as high (default pull-up state) */
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TRISB &= ~(SCL|SDA); /* set as output (it must be driven because there is no pull-up */
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LATB |= SCL|SDA; /* set as high (default pull-up state) */
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PEIE = 1; /* enable peripheral interrupt (for timer 2) */
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GIE = 1; /* golablly enable interrupts */
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@ -161,11 +161,14 @@ static void interrupt(void) __interrupt 0
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if (switches&SWITCH1) { /* switch 1 changed */
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if (PORTB&SWITCH1) { /* switch 1 released */
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led_off(); /* reset LED */
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i2c_write_byte(1,0,0xa0);
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i2c_write_byte(0,1,0xa0);
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// i2c_write_byte(0,1,0x17);
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// i2c_write_byte(1,0,0xa1);
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// i2c_read_byte(0,0);
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send_start();
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send_byte(0xa0);
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send_byte(0x1c);
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send_byte(0x17);
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send_start();
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send_byte(0xa1);
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read_byte();
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send_stop();
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} else { /* switch 1 pressed */
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led_on(); /* test LED */
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}
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