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          EEPW首頁 > 手機(jī)與無線通信 > 設(shè)計(jì)應(yīng)用 > 基于pic單片機(jī)的模擬I2C通信

          基于pic單片機(jī)的模擬I2C通信

          作者: 時(shí)間:2011-05-28 來源:網(wǎng)絡(luò) 收藏

          本文引用地址:http://www.ex-cimer.com/article/156255.htm

          ;+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
          ; File Name: i2c_low.asm
          ; Author: Alan G. Smith
          ; Purpose: This code is borrowed from Microchip with all of the fancy
          ; stuff taken out.
          ;+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

          InitBusMaster

          ;************************************************************
          TxmtStartBit
          bsf Bus_Busy ; on a start condition bus is busy
          bsf STATUS, RP0 ; Select page 1
          bsf _SDA ; set SDA high
          bsf _SCL ; clock is high
          call Delay40uSec ; This is necessary for setup time
          bcf _SDA ; This gives a falling edge on SDA while clock is high
          call Delay47uSec ; Necessary for START HOLD time
          return
          ;************************************************************
          TxmtStopBit
          bsf STATUS, RP0 ; Select page 1
          bcf _SCL ; clock is low
          bcf _SDA ; set SDA low
          bsf _SCL ; clock is pulled up
          call Delay40uSec ; Setup time for STOP condition
          bsf _SDA ; rising edge on SDA while CLOCK is high
          call Delay47uSec ; makes sure a START isn‘t sent immediately after a STOP
          bcf Bus_Busy ; The bus isn‘t busy anymore
          return
          ;************************************************************
          Abort
          call TxmtStopBit ; Send a stop bit
          bsf Abort ; set the abort bit
          return
          ;************************************************************
          TxmtSlaveAddr
          movf SlaveAddr, w ; Move slave address to W
          bcf ACK_Error ; reset Acknowledge error bit
          movwf Data ; move W to I2C Data
          bcf I2CData, LSB ; Set for write
          btfsc Slave_RW ; If skip then write operation
          bsf I2CData, LSB ; Clear for read
          call SendData ; send the address
          btfss Txmt_Success ; skip if successful
          goto AddrSendFail ; Oops, we failed
          retlw TRUE ; return true
          AddrSendFail
          btfss ACK_Error ; was there an error acknowledging
          retlw FALSE ; No, so return 0
          call TxmtStopBit ; Address not acknowleged, so send STOP bit
          retlw FALSE ; Unsuccessful, so return 0

          ;************************************************************
          SendData
          ; We might should make a copy of the data here, the example does but I don‘t see why!!!
          bsf Txmt_Progress ; We are in the middle of transmitting
          bcf Txmt_Success ; reset success bit
          movlw 0x08
          movwf I2CBitCount ; Set I2C Bit Count to 8
          bsf STATUS, RP0 ; Select page 1
          TxmtNextBit:
          bcf _SCL ; Set clock Low
          rlf I2CData, F ; MSB First, Note that I2CData is Destroyed
          bcf _SDA ; Set clock based on what the MSB is
          btfsc STATUS,C ; Was the MSB a 1
          bsf _SDA ; Nope set it high
          call Delay47uSec ; guarantee min LOW TIME tLOW Setup time
          bsf _SCL ; set clock high
          call Delay40uSec ; guarantee min HIGH TIME tHIGH
          decfsz I2CBitCount, F ; are we done yet
          goto TxmtNextBit ; nope, send the next bit
          ;
          ; Check For Acknowledge
          ;
          bcf _SCL ; reset clock
          bsf _SDA ; Release SDA line for Slave to pull down
          call Delay47uSec ; guarantee min LOW TIME tLOW Setup time
          bsf _SCL ; clock for slave to ACK
          call Delay40uSec ; guarantee min HIGH TIME tHIGH
          bcf STATUS, RP0 ; Select PAGE 0 to test SDA pin
          btfsc SdaPin ; SDA should be pulled low by slave if OK
          goto TxmtErrorAck ; Uh oh, slave isn‘t behaving (or isn‘t there)
          bsf STATUS, RP0 ; Select PAGE 1
          bcf _SCL ; reset clock
          bcf Txmt_Progress ; reset progress bit in Bus Status
          bsf Txmt_Success ; Transmission successful
          bcf ACK_Error ; ACK OK
          return
          TxmtErrorAck
          bsf STATUS,RP0 ; select page 1
          bsf _SDA ; tristate SDA
          bsf _SCL ; tristate SCL
          bcf Txmt_Progress ; reset progress bit in Bus Status
          bcf Txmt_Success ; Transmission NOT successful
          bsf ACK_Error ; No ACK From Slave
          return

          ;************************************************************
          GetData
          bsf Rcv_Progress ; set Bus status for txmt progress
          bcf Rcv_Success ; reset status bit
          movlw 0x08
          movwf I2CBitCount
          RcvNextBit
          bsf STATUS, RP0 ; page 1 for TRIS manipulation
          bcf _SCL ; lower clock
          bcf _SDA ; lower data line
          call Delay47uSec ; guarantee min LOW TIME tLOW setup time
          bsf _SCL ; clock high, data sent by slave
          call Delay40uSec ; guarantee min HIGH TIME tHIGH
          bcf STATUS, RP0 ; select page 0 to read Ports
          bcf STATUS, C ; 0 out Status
          btfsc SdaPin ; Check state of pin
          bsf STATUS, C ; Pin was high, set status
          rlf I2CData, F ; left Shift data (MSB first)
          decfsz I2CBitCount, F ; Are we done yet
          goto RcvNextBit ; Nope, go get the next one
          ;
          ; Generate ACK bit if not last byte to be read,
          ; if last byte Gennerate NACK ; do not send ACK on last byte, main routine will send a STOP bit
          ;
          bsf STATUS, RP0 ; Page 1 for TRIS manipulation
          bcf _SCL ; pull SCL low
          bcf _SDA ; ACK by pulling SDA low
          btfsc Last_Byte_Rcv ; Is it the last byte to receive
          bsf _SDA ; If so, send NACK by setting SDA high
          call Delay47uSec ; guarantee min LOW TIME tLOW Setup time
          bsf _SCL ; Raise Clock back up
          call Delay40uSec ; guarantee min HIGH TIME tHIGH
          RcvEnd:
          bcf _SCL ; reset clock
          bcf Rcv_Progress ; reset bit in Bus Status
          bsf Rcv_Success ; transmission successful
          bcf ACK_Error ; ACK OK
          return


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