Subversion Repositories group.electronics

;---------------------------------------------------------------------
; File: an734_PIC16.asm
;
; Written By: Stephen Bowling, Microchip Technology
;
; Version: 1.00
;
; Assembled using Microchip Assembler
;
; Functionality:
;
; This code implements the basic functions for an I2C slave device
; using the SSP module. All I2C functions are handled in an ISR.
; Bytes written to the slave are stored in a buffer. After a number
; of bytes have been written, the master device can then read the
; bytes back from the buffer.
;
; Variables and Constants used in the program:
;
; The start address for the receive buffer is stored in the variable
; 'RXBuffer'. The length of the buffer is denoted by the constant
; value 'RX_BUF_LEN'. The current buffer index is stored in the
; variable 'Index'.
;
;--------------------------------------------------------------------
;
; The following files should be included in the MPLAB project:
;
; an734_PIC16.asm-- Main source code file
;
; 16f877a.lkr-- Linker script file
; (change this file for the device you are using)
;
;---------------------------------------------------------------------
;---------------------------------------------------------------------
; Include Files
;---------------------------------------------------------------------
list        p=16F88
#include <p16f88.inc> ; Change to device that you are using.
        __CONFIG        _CONFIG1, _CP_OFF & _CCP1_RB3 & _CCPMX_RB3 & _DEBUG_OFF & _WRT_PROTECT_OFF & _CPD_OFF & _LVP_OFF & _BODEN_OFF & _MCLR_ON & _PWRTE_ON & _WDT_ON & _HS_OSC
        ERRORLEVEL -302
;---------------------------------------------------------------------
;Constant Definitions
;---------------------------------------------------------------------
#define NODE_ADDR 0x4e ; I2C address of slave 2

    #define LED0         PORTA,0
    #define LED1         PORTA,1
    #define LED2         PORTA,2
    #define LED3         PORTA,3
    #define LED4         PORTA,4
    #define LED5         PORTB,2
    #define LED6         PORTB,0
    #define LED7         PORTB,5
; Change this value to address that
; you wish to use.
;---------------------------------------------------------------------
; Buffer Length Definition
;---------------------------------------------------------------------
#define RX_BUF_LEN 8 ; Length of receive buffer
;---------------------------------------------------------------------
; Variable declarations
;---------------------------------------------------------------------
    udata_shr
    WREGsave    res 1
    RXBuffer    res RX_BUF_LEN
      

    udata
    STATUSsave  res 1
    FSRsave     res 1
    PCLATHsave  res 1
    Index       res 1           ; Index to receive buffer
    Temp        res 1           ;

    
; device.
;---------------------------------------------------------------------
; Vectors
;---------------------------------------------------------------------
STARTUP code 0x00
    nop
    goto    Startup ;
    nop             ; 0x0002
    nop             ; 0x0003
    goto    ISR     ; 0x0004
PROG code
;---------------------------------------------------------------------
; Macros
;---------------------------------------------------------------------
memset macro Buf_addr,Value,Length
    movlw   Length      ; This macro loads a range of data memory
    movwf   Temp        ; with a specified value. The starting
    movlw   Buf_addr    ; address and number of bytes are also
    movwf   FSR         ; specified.
SetNext movlw Value
    movwf   INDF
    incf    FSR,F
    decfsz  Temp,F
    goto    SetNext
    endm
LFSR macro Address,Offset   ; This macro loads the correct value
    movlw   Address         ; into the FSR given an initial data
    movwf   FSR             ; memory address and offset value.
    movf    Offset,W
    addwf   FSR,F
    endm
;---------------------------------------------------------------------
; Main Code
;---------------------------------------------------------------------
Startup
    bcf     STATUS,RP1
    bsf     STATUS,RP0
    call    Setup
    banksel WREGsave
    banksel RXBuffer
    clrf    RXBuffer
        bcf     LED0
        bcf     LED1
        bcf     LED2
        bcf     LED3
        bcf     LED4
        bcf     LED5
        bcf     LED6
        bcf     LED7

Main clrwdt ; Clear the watchdog timer.
    banksel PORTB
    btfsc   RXBuffer,0
    bsf     LED0
    btfss   RXBuffer,0
    bcf     LED0

    btfsc   RXBuffer,1
    bsf     LED1
    btfss   RXBuffer,1
    bcf     LED1

    btfsc   RXBuffer,2
    bsf     LED2
    btfss   RXBuffer,2
    bcf     LED2

    btfsc   RXBuffer,3
    bsf     LED3
    btfss   RXBuffer,3
    bcf     LED3

    btfsc   RXBuffer,4
    bsf     LED4
    btfss   RXBuffer,4
    bcf     LED4

    btfsc   RXBuffer,5
    bsf     LED5
    btfss   RXBuffer,5
    bcf     LED5

    btfsc   RXBuffer,6
    bsf     LED6
    btfss   RXBuffer,6
    bcf     LED6

    btfsc   RXBuffer,7
    bsf     LED7
    btfss   RXBuffer,7
    bcf     LED7

    goto    Main ; Loop forever.
;---------------------------------------------------------------------
; Interrupt Code
;---------------------------------------------------------------------
ISR
    movwf   WREGsave    ; Save WREG
    movf    STATUS,W    ; Get STATUS register
    banksel STATUSsave  ; Switch banks, if needed.
    movwf   STATUSsave  ; Save the STATUS register
    movf    PCLATH,W    ;
    movwf   PCLATHsave  ; Save PCLATH
    movf    FSR,W       ;
    movwf   FSRsave     ; Save FSR
    banksel PIR1
    btfss   PIR1,SSPIF  ; Is this a SSP interrupt?
    goto    $           ; No, just trap here.
    bcf     PIR1,SSPIF
    call    SSP_Handler ; Yes, service SSP interrupt.
    banksel FSRsave
    movf    FSRsave,W   ;
    movwf   FSR         ; Restore FSR
    movf    PCLATHsave,W;
    movwf   PCLATH      ; Restore PCLATH
    movf    STATUSsave,W;
    movwf   STATUS      ; Restore STATUS
    swapf   WREGsave,F  ;
    swapf   WREGsave,W  ; Restore WREG
    retfie              ; Return from interrupt.
;---------------------------------------------------------------------
Setup
;
; Initializes program variables and peripheral registers.
;---------------------------------------------------------------------
    banksel PCON
    bsf     PCON,NOT_POR
    bsf     PCON,NOT_BOR
    banksel ANSEL
    movlw   0x00
    movwf   ANSEL
    banksel Index       ; Clear various program variables
    clrf    Index
    clrf    PORTB
    clrf    PIR1
    banksel TRISB
    clrf    TRISB
    bsf     TRISB,4
    bsf     TRISB,1

    banksel TRISA
    clrf    TRISA
    movlw   0x36        ; Setup SSP module for 7-bit
    banksel SSPCON
    movwf   SSPCON      ; address, slave mode
    movlw   NODE_ADDR
    banksel SSPADD
    movwf   SSPADD
    clrf    SSPSTAT
    banksel PIE1        ; Enable interrupts
    bsf     PIE1,SSPIE
    bsf     INTCON,PEIE ; Enable all peripheral interrupts
    bsf     INTCON,GIE  ; Enable global interrupts
    bcf     STATUS,RP0
    return
;---------------------------------------------------------------------
SSP_Handler

;---------------------------------------------------------------------
; The I2C code below checks for 5 states:
;---------------------------------------------------------------------
; State 1: I2C write operation, last byte was an address byte.
; SSPSTAT bits: S = 1, D_A = 0, R_W = 0, BF = 1
;
; State 2: I2C write operation, last byte was a data byte.
; SSPSTAT bits: S = 1, D_A = 1, R_W = 0, BF = 1
;
; State 3: I2C read operation, last byte was an address byte.
; SSPSTAT bits: S = 1, D_A = 0, R_W = 1 (see Appendix C for more information)
;
; State 4: I2C read operation, last byte was a data byte.
; SSPSTAT bits: S = 1, D_A = 1, R_W = 1, BF = 0
;
; State 5: Slave I2C logic reset by NACK from master.
; SSPSTAT bits: S = 1, D_A = 1, BF = 0 (see Appendix C for more information)
;
; For convenience, WriteI2C and ReadI2C functions have been used.
;----------------------------------------------------------------------
    banksel SSPSTAT
    movf    SSPSTAT,W   ; Get the value of SSPSTAT
    andlw   b'00101101' ; Mask out unimportant bits in SSPSTAT.
    banksel Temp        ; Put masked value in Temp
    movwf   Temp        ; for comparision checking.
State1:                 ; Write operation, last byte was an   
    movlw   b'00001001' ; address, buffer is full.
    xorwf   Temp,W      ;
    btfss   STATUS,Z    ; Are we in State1?
    goto    State2      ; No, check for next state.....
    memset RXBuffer,0,RX_BUF_LEN ; Clear the receive buffer.
    clrf    Index       ; Clear the buffer index.
    banksel SSPBUF      ; Do a dummy read of the SSPBUF.
    movf    SSPBUF,W
    return
State2:                 ; Write operation, last byte was data,
    movlw   b'00101001' ; buffer is full.
    xorwf   Temp,W
    btfss   STATUS,Z    ; Are we in State2?
    goto    State3      ; No, check for next state.....
    LFSR RXBuffer,Index ; Point to the buffer.
    banksel SSPBUF      ; Get the byte from the SSP.
    movf    SSPBUF,W
    movwf   INDF        ; Put it in the buffer.
    incf    Index,F     ; Increment the buffer pointer.
    movf    Index,W     ; Get the current buffer index.
    sublw   RX_BUF_LEN  ; Subtract the buffer length.
    btfsc   STATUS,Z    ; Has the index exceeded the buffer length?
    clrf    Index       ; Yes, clear the buffer index.
    return
State3:                 ; Read operation, last byte was an address,
    movf    Temp,W ;
    andlw   b'00101100' ; Mask BF bit in SSPSTAT
    xorlw   b'00001100'
    btfss   STATUS,Z    ; Are we in State3?
    goto    State4      ; No, check for next state.....
    clrf    Index       ; Clear the buffer index.
    LFSR RXBuffer,Index ; Point to the buffer
    movf    INDF,W      ; Get the byte from buffer.
    call    WriteI2C    ; Write the byte to SSPBUF
    incf    Index,F     ; Increment the buffer index.
    return
State4:                 ; Read operation, last byte was data,
    banksel SSPCON      ; buffer is empty.
    btfsc   SSPCON, CKP
    goto    State5

    movlw   b'00101100'
    xorwf   Temp,W
    btfss   STATUS,Z    ; Are we in State4?
    goto    State5      ; No, check for next state....
    movf    Index,W     ; Get the current buffer index.
    sublw   RX_BUF_LEN  ; Subtract the buffer length.
    btfsc   STATUS,Z    ; Has the index exceeded the buffer length?
    clrf    Index       ; Yes, clear the buffer index.
    LFSR RXBuffer,Index ; Point to the buffer
    movf    INDF,W      ; Get the byte
    call    WriteI2C    ; Write to SSPBUF
    incf    Index,F     ; Increment the buffer index.
    return

State5:
    movf    Temp,W      ; NACK received when sending data to the master
    andlw   b'00101000' ; Mask RW bit in SSPSTAT
    xorlw   b'00101000' ;
    btfss   STATUS,Z    ;
    goto    I2CErr  ;
    return              ; If we aren?t in State5, then something is
                        ; wrong.
I2CErr nop
    banksel PORTB       ; Something went wrong! Set LED
    bsf     PORTB,2     ; and loop forever. WDT will reset
    goto    $           ; device, if enabled.
    return
;---------------------------------------------------------------------
; WriteI2C
;---------------------------------------------------------------------
WriteI2C
    banksel SSPSTAT
    btfsc   SSPSTAT,BF  ; Is the buffer full?
    goto    WriteI2C    ; Yes, keep waiting.
    banksel SSPCON      ; No, continue.
DoI2CWrite
    bcf     SSPCON,WCOL ; Clear the WCOL flag.
    movwf   SSPBUF      ; Write the byte in WREG
    btfsc   SSPCON,WCOL ; Was there a write collision?
    goto    DoI2CWrite
    bsf     SSPCON,CKP  ; Release the clock.
    return

end