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