HARDWARE I2C SAMPLE CODE question

[Michael Wakileh]

Hi! I just found some nice code from microchip showing a simple write/read sequence to an I2C EEPROM using MSSP in mastermode. The code is well documented so I feel I will be able to use parts of it to replace PBP statements
even though I don't speak assembly language... Unfortunately I'm not at a computer where I can test, and I have a simple question...

In the code there are certain define statements-and it looks
like they are in some other compiler language....or are these in assembly?

; I2C connected to 24C01C (or similar) EEPROM.
; Write to location 0x12, data 0x34 and read it back.
; The MSSP module is used in I2C MASTER mode.

#define LC01CTRLIN H'A0’ ; I2C value for CONTROL BYTE when!!!!!!!!!!!!!!!!!!!!!!!!!CONTROLBYTE for write
; INputing data to the EEPROM

#define LC01CTRLOUT H'A1’ ; I2C value for CONTROL BYTE when!!!!!!!!!!!!!!!!!!!!!!!!CONTROIBYTE for read
; requesting OUTput from the EEPROM

#define LC01ADDR H'12’ ; Sample value for ADDRESS BYTE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!Address byte
#define LC01DATA H’34’ ; Sample data to write to EEPROM!!!!!!!!!!!!!!!!!!!!!!!!!!!!Data to write to Address
#define BAUD D'100’ ; Desired Baud Rate in kbps
#define FOSC D'4000’ ; Oscillator Clock in kHz

#include <p16F877.inc> ; Processor Include file, for standard names
__CONFIG _CP_OFF & _DEBUG_OFF & _WRT_ENABLE_OFF & _CPD_OFF & _LVP_OFF &
_BODEN_OFF & _PWRTE_ON & _WDT_OFF & _XT_OSC
ORG 0 ; Start of code (location 0)


; *** Setup I/O ***

clrf PORTB 		; PORTB pins set to drive low when enabled
BANKSEL TRISC 		; BANK 1
movlw B'00011000’ 	; RC3, RC4 are inputs for PORTC
movwf TRISC 		; Remaining PORTC I/O lines are outputs
clrf TRISB 		; all PORTB pins configured for output mode
			; (enables all PORTB drivers for driving LEDs)


; *** Setup Registers for I2C ***
; Configure MSSP module for Master Mode

BANKSEL SSPCON
movlw B'00101000’ 	; Enables MSSP and uses appropriate
			; PORTC pins for I2C mode (SSPEN set) AND
			; Enables I2C Master Mode (SSPMx bits)
movwf SSPCON 		; This is loaded into SSPCON
			; Configure Input Levels and slew rate as I2C Standard Levels
BANKSEL SSPSTAT
movlw B'10000000’ 	; Slew Rate control (SMP) set for 100kHz
movwf SSPSTAT 		; mode and input levels are I2C spec,
			; loaded in SSPSTAT


; Configure Baud Rate
BANKSEL SSPADD

movlw (FOSC / (4 * BAUD)) - 1 ; Calculates SSPADD Setting for
movwf SSPADD ; desired Baud rate and sets up SSPADD




; *** Begin I2C Data Transfer Sequences ***
I2CWrite
; Send START condition and wait for it to complete

BANKSEL SSPCON2 		; BANK 1
bsf SSPCON2,SEN 		; Generate START Condition
call WaitMSSP 			; Wait for I2C operation to complete

; Send and Check CONTROL BYTE, wait for it to complete
movlw LC01CTRLIN 		; Load CONTROL BYTE (input mode)
call Send_I2C_Byte 		; Send Byte
call WaitMSSP 			; Wait for I2C operation to complete
BANKSEL SSPCON2
btfsc SSPCON2,ACKSTAT 		; Check ACK Status bit to see if I2C
goto I2CFail 			; failed, skipped if successful

; Send and Check ADDRESS BYTE, wait for it to complete
movlw LC01ADDR 		; Load Address Byte
call Send_I2C_Byte 		; Send Byte
call WaitMSSP 			; Wait for I2C operation to complete
BANKSEL SSPCON2
btfsc SSPCON2,ACKSTAT 		; Check ACK Status bit to see if I2C
goto I2CFail 			; failed, skipped if successful

; Send and Check DATA BYTE, wait for it to complete
movlw LC01DATA 			; Load Data Byte
call Send_I2C_Byte 		; Send Byte
call WaitMSSP 			; Wait for I2C operation to complete
BANKSEL SSPCON2
btfsc SSPCON2,ACKSTAT 		; Check ACK Status bit to see if I2C
goto I2CFail 			; failed, skipped if successful

; Send and Check the STOP condition, wait for it to complete
BANKSEL SSPCON2
bsf SSPCON2,PEN 		; Send STOP condition
call WaitMSSP 			; Wait for I2C operation to complete

; The WRITE has now completed successfully. Begin the Read Sequence


++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

I2C READ
; Send RESTART condition and wait for it to complete

BANKSEL SSPCON2
bsf SSPCON2,RSEN 	; Generate RESTART Condition
call WaitMSSP 		; Wait for I2C operation to complete

; Send and Check CONTROL BYTE, wait for it to complete
movlw LC01CTRLIN 		; Load CONTROL BYTE (input)
call Send_I2C_Byte 		; Send Byte
call WaitMSSP 			; Wait for I2C operation to complete

; Now check to see if I2C EEPROM is ready
BANKSEL SSPCON2
btfsc SSPCON2,ACKSTAT 		; Check ACK Status bit to see if I2C
goto I2CRead 		; ACK Poll waiting for EEPROM write to complete

; Send and Check ADDRESS BYTE, wait for it to complete
movlw LC01ADDR 			; Load ADDRESS BYTE
call Send_I2C_Byte 		; Send Byte
call WaitMSSP 			; Wait for I2C operation to complete
BANKSEL SSPCON2
btfsc SSPCON2,ACKSTAT 		; Check ACK Status bit to see if I2C
goto I2CFail 			; failed, skipped if successful

; Send REPEATED START condition and wait for it to complete
bsf SSPCON2,RSEN 		; Generate REPEATED START Condition
call WaitMSSP 			; Wait for I2C operation to complete

; Send and Check CONTROL BYTE (out), wait for it to complete
movlw LC01CTRLOUT 		; Load CONTROL BYTE (output)
call Send_I2C_Byte 		; Send Byte
call WaitMSSP 			; Wait for I2C operation to complete
BANKSEL SSPCON2
btfsc SSPCON2,ACKSTAT 		; Check ACK Status bit to see if I2C
goto I2CFail 			; failed, skipped if succe
ssful

; Switch MSSP module to I2C Receive mode
bsf SSPCON2,RCEN 		; Enable Receive Mode (I2C)

; Get the DATA BYTE and wait for it to complete. Data is in SSPBUF when done.

; The receive mode is disabled at end automatically by the MSSP module.

call WaitMSSP 			; Wait for I2C operation to complete

; Send NACK bit for Acknowledge Sequence
BANKSEL SSPCON2
bsf SSPCON2,ACKDT 		; ACK DATA to send is 1, which is NACK.
bsf SSPCON2,ACKEN 		; Send ACK DATA now.

; Once ACK or NACK is sent, the ACKEN is automatically cleared by the MSSP
; Send and Check the STOP condition and wait for it to complete.

bsf SSPCON2,PEN 		; Send STOP condition
call WaitMSSP 			; Wait for I2C operation to complete


; I2C Write and Read have both finished, the value is output on LEDs.
BANKSEL SSPBUF 			; BANK 0
movf SSPBUF,W 			; Get data from SSPBUF into W register
movwf PORTB 			; Output W register to LEDs on PORTB


; Program has finished and completed successfully.
goto $ 				; Wait forever at this location!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!CHANGE THIS



; *** SUBROUTINES & ERROR HANDLERS ***


; I2C Operation Failed code sequence - This will normally not happen,
; but if it does, a STOP is sent and the entire code is tried again.

I2CFail
BANKSEL SSPCON2
bsf SSPCON2,PEN 		; Send STOP condition
call WaitMSSP 			; Wait for I2C operation to complete
BANKSEL PORTB 			; BANK 0
movlw 0xFF 			; Turn on all LEDs on PORTB
movwf PORTB 			; to show error condition
goto $ 				; Wait forever at this location!!!!!!!!!!!!!!!!!!!!!!!!!!!!!CHANGE THIS





; This routine sends the W register to SSPBUF, thus transmitting a byte.
; Then, the SSPIF flag is checked to ensure the byte has been sent successfully.
; When that has completed, the routine exits, and executes normal code.

Send_I2C_Byte
BANKSEL SSPBUF 			; BANK 0
movwf SSPBUF 			; Get value to send from W, put in SSPBUF
retlw 0 			; Done, Return 0



; This routine waits for the last I2C operation to complete.
; It does this by polling the SSPIF flag in PIR1.
;!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!BUT HOW TO DO THIS CODE IN THE BACKGROUND???

WaitMSSP
BANKSEL PIR1 			; BANK 0
btfss PIR1,SSPIF 		; Check if done with I2C operation
goto $-1 			; I2C module is not ready yet
bcf PIR1,SSPIF			; I2C module is ready, clear flag.
Retlw 0 			; Done, Return 0
END

[Melanie]

What you see is Microchip Assembler.

[Michael Wakileh]

thanks Mel!