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THE COMPANY SHALL NOT, ;IN ANY CIRCUMSTANCES, BE LIABLE FOR SPECIAL, INCIDENTAL OR ;CONSEQUENTIAL DAMAGES, FOR ANY REASON WHATSOEVER. ; ******************************************************************* ; I2CBUS.ASM ; This file contains the routines necessary to bit-bang an I2C interface ; on a mid-range PICmicro device. ; Best Case Timings: ; ; I2C_ReceiveByte 246 cycles ; I2C_StartBit 11 cycles ; I2C_StopBit 16 cycles ; I2C_SendACK 20 cycles ; I2C_SendNAK 20 cycles ; I2C_TransmitByte 227 cycles ; Version Date Description ;-------------------------------------------------------------------- ; 0.00.01 xx-Dec-2004 KLO Initial Release #include "project.inc" global I2C_ErrorCode global I2C_Flags global I2C_ReceiveByte global I2C_StartBit global I2C_StopBit global I2C_SendACK global I2C_SendNAK global I2C_TransmitByte #define I2C_BUS_BUSY_CLOCK 1 ; Clock locked low by device (bus is still busy) #define I2C_BUS_BUSY_DATA 2 ; Data locked low by device (bus is still busy) #define I2C_NO_ACK 3 ; No acknowledge from device (no handshake) #define I2C_NO_STOP 4 ; Data bus not released for master to generate STOP bit #define I2C_INPUT_BIT 7 ; I2C_TempBuffer bit number of current input bit value #define I2C_OUTPUT_BIT 6 ; I2C_TempBuffer bit number of current output bit value #define I2C_ERROR_BIT 0 ; I2C_Flags error indicator bit ; udata_shr udata I2C_Counter res 1 I2C_ErrorCode res 1 I2C_Flags res 1 I2C_ReceiveBuffer res 1 I2C_TransmitBuffer res 1 I2C_TempBuffer res 1 code ;----------------------------------------------------------------------------- ; I2C_Error ; ; This routine is called when an error has occurred. If there is currently ; no error, then store this error code and set the error flag bit. ; ; code error status mode ; ------- ------------------------------------------------------ ; 1 : SCL locked low by device (bus is still busy) ; 2 : SDA locked low by device (bus is still busy) ; 3 : No acknowledge from device (no handshake) ; 4 : SDA bus not released for master to generate STOP bit ; ; Input : WREG ErrorCode ; Output : I2C_ErrorCode Error code ; Affects : none ; Time : 5 cycles ;----------------------------------------------------------------------------- I2C_Error btfss I2C_Flags, I2C_ERROR_BIT ; If we do not currently movwf I2C_ErrorCode ; have an error code stored, bsf I2C_Flags, I2C_ERROR_BIT ; store this one and set the ; error flag. retlw 0 ;----------------------------------------------------------------------------- ; I2C_StartBit ; ; This routine generates a start bit to begin communication. A start bit is ; characterized by the data line going from high to low while the clock line ; is high. If we cannot successfully drive the clock line high, then the bus ; is busy, and we report an error. ; ; Input : none ; Output : none ; Affects : none ; Time : 17 cycles with errors ; 11 cycles with no errors ;----------------------------------------------------------------------------- I2C_StartBit bsf I2C_DATA ; Set the data and clock lines high bsf I2C_CLOCK ; to begin the start bit. movlw I2C_BUS_BUSY_CLOCK ; If we cannot drive the clock line btfss I2C_CLOCK ; high, report an error. call I2C_Error bcf I2C_DATA ; Set the data line low, and then nop ; set the clock line low to end the nop ; start bit. bcf I2C_CLOCK retlw 0 ;----------------------------------------------------------------------------- ; I2C_StopBit ; ; This routine generates a stop bit to end communications. A stop bit is ; characterized by the data line going from low to high while the clock line ; is high. If we cannot successfully drive the clock or the data line high, ; then the bus is busy, and we report an error. ; ; Input : none ; Output : none ; Affects : none ; Time : 28 cycles with errors ; 16 cycles with no errors ;----------------------------------------------------------------------------- I2C_StopBit bcf I2C_DATA ; Set the data line low and the bsf I2C_CLOCK ; clock line high to begin the stop nop ; bit. nop movlw I2C_BUS_BUSY_CLOCK ; If we cannot drive the clock line btfss I2C_CLOCK ; high, report an error. call I2C_Error bsf I2C_DATA ; Set the data line high. nop nop nop movlw I2C_NO_STOP ; If we cannot drive the data line btfss I2C_DATA ; high, report an error. call I2C_Error retlw 0 ;----------------------------------------------------------------------------- ; I2C_BitIn ; ; This routine receives one data bit from the bus and places it in the ; temporary input buffer. The data bit is read by driving the clock high, ; reading the data bit, and then setting the clock low. If we cannot drive ; the clock high, then we report an error. ; ; Input : none ; Output : I2C_TempBuffer I2C_INPUT_BIT is new data bit ; Affects : WREG destroyed ; Time : 27 cycles with errors ; 21 cycles with no errors ;----------------------------------------------------------------------------- I2C_BitIn movlw I2C_TRIS_DATA_IN ; Set the data line to an input. bsf STATUS, RP0 ; Make sure we do not drive the line errorlevel -302 ; low. movwf I2C_TRIS bcf STATUS, RP0 errorlevel +302 bsf I2C_DATA bcf I2C_TempBuffer, I2C_INPUT_BIT bsf I2C_CLOCK ; Set the clock line high to clock movlw I2C_BUS_BUSY_CLOCK ; out the bit. If we cannot drive it btfsc I2C_CLOCK ; high, report an error. goto I2C_BitInRead call I2C_Error I2C_BitInRead btfsc I2C_DATA ; Read the data line, and bsf I2C_TempBuffer, I2C_INPUT_BIT ; set the buffer bit to nop ; match. Then return the clock bcf I2C_CLOCK ; to low. movlw I2C_TRIS_DATA_OUT ; Set the data line to an output. bsf STATUS, RP0 errorlevel -302 movwf I2C_TRIS bcf STATUS, RP0 errorlevel +302 retlw 0 ;----------------------------------------------------------------------------- ; I2C_BitOut ; ; This routine takes the data bit from the temporary input buffer and sends it ; on the bus. The data bit is sent by setting the data line, then driving the ; clock line high then low. If we cannot drive the clock or data line high, ; then we report an error. ; ; Input : I2C_TempBuffer I2C_OUTPUT_BIT is transmitted data bit ; Output : none ; Affects : WREG destroyed ; Time : 29 cycles with errors ; 15 cycles with no errors ;----------------------------------------------------------------------------- I2C_BitOut btfss I2C_TempBuffer, I2C_OUTPUT_BIT ; See if we need to send a goto I2C_BitOutLow ; 1 or a 0. bsf I2C_DATA ; Send a high bit. If we can't movlw I2C_BUS_BUSY_DATA ; drive it high, give an error. btfsc I2C_DATA goto I2C_BitOutClock call I2C_Error goto I2C_BitOutClock I2C_BitOutLow bcf I2C_DATA ; Send a low bit. nop I2C_BitOutClock bsf I2C_CLOCK ; Set the clock high. If we can't movlw I2C_BUS_BUSY_CLOCK ; drive it high, give an error. btfsc I2C_CLOCK goto I2C_BitOutDone call I2C_Error I2C_BitOutDone bcf I2C_CLOCK ; Return the clock to low. retlw 0 ;----------------------------------------------------------------------------- ; I2C_SendACK ; ; This routine sends an acknowledge bit. ; ; Input : none ; Output : none ; Affects : WREG destroyed ; Time : 5 + I2C_BitOut = 34 cycles with errors ; 20 cycles with no errors ;----------------------------------------------------------------------------- I2C_SendACK bcf I2C_TempBuffer, I2C_OUTPUT_BIT ; Set the acknowledge bit to call I2C_BitOut ; to stop further input. retlw 0 ;----------------------------------------------------------------------------- ; I2C_SendNAK ; ; This routine sends a negative acknowledge bit. ; ; Input : none ; Output : none ; Affects : WREG destroyed ; Time : 5 + I2C_BitOut = 34 cycles with errors ; 20 cycles with no errors ;----------------------------------------------------------------------------- I2C_SendNAK bsf I2C_TempBuffer, I2C_OUTPUT_BIT ; Set the acknowledge bit to call I2C_BitOut ; to stop further input. retlw 0 ;----------------------------------------------------------------------------- ; I2C_ReadACK ; ; This routine reads an acknowledge bit. If an acknowledge bit is not ; received, an error is reported. ; ; Input : none ; Output : none ; Affects : WREG destroyed ; Time : 8 + I2C_BitIn + I2C_Error = 40 cycles with errors ; 7 + I2C_BitIn = 28 cycles with no errors ;----------------------------------------------------------------------------- I2C_ReadACK call I2C_BitIn ; Read the acknowledge bit. If there movlw I2C_NO_ACK ; is no acknowledgement, set an error. btfsc I2C_TempBuffer, I2C_INPUT_BIT call I2C_Error retlw 0 ;----------------------------------------------------------------------------- ; I2C_ReceiveByte ; ; This routine receives one byte from the bus. It calls the routine I2C_BitIn ; once for each bit, and rotates each new bit into the receive buffer. No ; acknowledge bit is sent or read, since the master might need to send ; either an ACK or a NAK. ; ; Input : none ; Output : WREG Received data byte ; Affects : none ; Time : 6 + 8*(9+I2C_BitIn) = 294 cycles with errors ; = 246 cycles with no errors ;----------------------------------------------------------------------------- I2C_ReceiveByte movlw 8 ; Get ready to shift in 8 bits of data. movwf I2C_Counter clrf I2C_ReceiveBuffer RXLP bcf STATUS, C ; Rotate the input byte to get ready rlf I2C_ReceiveBuffer, f ; for the next bit. Get the bit, and call I2C_BitIn ; copy it into the receive buffer. btfsc I2C_TempBuffer, I2C_INPUT_BIT bsf I2C_ReceiveBuffer,0 decfsz I2C_Counter, f ; If we have not read 8 bits, go back goto RXLP ; and get the next bit. movf I2C_ReceiveBuffer, w ; Put the received byte into W. return ;----------------------------------------------------------------------------- ; I2C_TransmitByte ; ; This routine transmits one byte on the bus. It calls the routine I2C_BitOut ; once for each bit. It then reads the acknowlegde bit. ; ; Input : WREG Data to transmit ; Output : none ; Affects : WREG destroyed ; Time : 7 + I2C_ReadACK + 8*(9+I2C_BitOut) = 351 cycles, errors ; 227 cycles, no errors ;----------------------------------------------------------------------------- I2C_TransmitByte movwf I2C_TransmitBuffer ; Store the byte to transmit. movlw 8 ; Get ready to shift out 8 bits. movwf I2C_Counter TXLP bcf I2C_TempBuffer, I2C_OUTPUT_BIT ; Copy the most significant btfsc I2C_TransmitBuffer, 7 ; bit of the transmit byte into bsf I2C_TempBuffer, I2C_OUTPUT_BIT ; the temporary buffer. Then call I2C_BitOut ; send it. rlf I2C_TransmitBuffer, f ; Get the next bit into position for ; sending. decfsz I2C_Counter, f ; If we haven't sent 8 bits yet, go goto TXLP ; back and send the next bit. call I2C_ReadACK retlw 0 end