; i2c.asm ; ; Copyright (C) 2006,2007 Nuno Sucena Almeida ; ; This program is free software; you can redistribute it and/or modify ; it under the terms of the GNU General Public License as published by ; the Free Software Foundation; either version 2 of the License, or ; (at your option) any later version. ; ; This program is distributed in the hope that it will be useful, ; but WITHOUT ANY WARRANTY; without even the implied warranty of ; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the ; GNU General Public License for more details. ; ; You should have received a copy of the GNU General Public License ; along with this program; if not, write to the Free Software ; Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA ; ; simple support for I2C interface in master mode operation ; see page 95 of 16F88 manual. include include udata i2c_register res 1 i2c_counter res 1 i2c_debug_counter res 1 ; i2c_status: ; bit 0 - i2c bus ACK read status (read by user,sent by slaves) ; bit 1 - i2c bus ACK set status (set by user,sent by master ) i2c_status res 1 ;-------------------------------------------------------------------- ; external functions extern delay10 extern uart_send extern uart_show_hex code ;-------------------------------------------------------------------- ; setup I2C communication ; see page 88ff,92 of the manual i2c_setup: banksel i2c_debug_counter clrf i2c_debug_counter ; 5 - SSPEN (enable SPI/I2C mode) ; 4 - CKP (enable Clock) ; <3:0> - 1011 I2C firmware controlled master mode (slave idle) movlw B'00111011' banksel SSPCON movwf SSPCON ;; free the clock and data i2c lines scl_HIGH sda_HIGH return ;-------------------------------------------------------------------- ; reads the i2c port data pin (SDA) and returns its value in 'W' i2c_read_sda: banksel PORTB btfsc SDA_IO retlw 1 retlw 0 ;-------------------------------------------------------------------- ; reads the i2c port clock pin (SCL) and returns its value in 'W' i2c_read_scl: banksel PORTB btfsc SCL_IO retlw 1 retlw 0 ;-------------------------------------------------------------------- ; send byte through the i2c bus, MSB first ; the user must provide the byte to send in 'W' ; see sequence for example on page 7 of 24AA512 datasheet ; or Philips I2C specification page 9,10 ; it sets the i2c ACK status flag if necessary i2c_send: ; put 'W' into a temp variable banksel i2c_register movwf i2c_register ; ; send debug to uart ; movlw A's' ; call uart_send ; movlw A'[' ; call uart_send ; we have 8 bits: movlw D'8' banksel i2c_counter movwf i2c_counter i2c_send_loop: ; set clock LOW scl_LOW ; rotate contents of register to the left and check the carry bit. banksel i2c_register rlf i2c_register,F ; if carry bit = 1, the bit was 1 btfss STATUS,C goto i2c_send_LOW i2c_send_HIGH: sda_HIGH goto i2c_send_loop_end i2c_send_LOW: sda_LOW i2c_send_loop_end: ; set clock HIGH so that the I2C slave loads the bit scl_HIGH banksel i2c_counter decfsz i2c_counter,F goto i2c_send_loop ;; read acknowledge bit from slave i2c_READ_ACK ; wait for clock line to be free i2c_SCL_WAIT ; ;; send debug to uart ; movlw A']' ; call uart_send return ;-------------------------------------------------------------------- ; receive byte from the i2c bus, MSB first ; and put the result in 'W' i2c_receive: ; clear receive register banksel i2c_register clrf i2c_register ; ; send debug to uart ; movlw A'r' ; call uart_send ; movlw A'[' ; call uart_send ; we have 8 bits: movlw D'8' banksel i2c_counter movwf i2c_counter ;; set data line to high impedance mode: sda_HIGH i2c_receive_loop: ; set clock LOW scl_LOW ; set clock HIGH scl_HIGH ; read bit,the value will be in the carry STATUS bit ; which will pass to the first bit of a left-rotated ; register i2c_READ banksel i2c_register ; rotate left rlf i2c_register,F banksel i2c_counter decfsz i2c_counter,F goto i2c_receive_loop ; send ACK to the slave i2c_WRITE_ACK ; ;; send debug to uart ; movlw A']' ; call uart_send ; put the result in 'W' banksel i2c_register movf i2c_register,W return ;-------------------------------------------------------------------- ; send debug info to uart i2c_debug: ;; show counter to more easily keep track of bits banksel i2c_debug_counter movf i2c_debug_counter,W call uart_show_hex banksel i2c_debug_counter incf i2c_debug_counter,F ;; Data movlw A'A' call uart_send movlw A'0' banksel PORTB btfsc SDA_IO movlw A'1' call uart_send ; movlw A' ' ; call uart_send ;; Clock movlw A'C' call uart_send movlw A'0' banksel PORTB btfsc SCL_IO movlw A'1' call uart_send movlw A' ' call uart_send return global i2c_setup global i2c_read_sda global i2c_read_scl global i2c_send global i2c_receive global i2c_debug global i2c_status end