RTC + PIC18 = <3

Here's my RTC sample code, ported for PIC18F4620. I added SSPIF support but disabled the interrupts and changed quite a bit of code in the basic I2C low-layer macros, including some #v()-literals to save space.

I wrote it in emacs, and have no clue how to use MPLAB. Sorry :)

Also note that it's relocatable code and full of my own debugging lines. You may have to play around with it to get it to work with your code. But it does definitely work the way it is now.

Cheers, Seb

i2c_common.asm

#include <p18f4620.inc>

errorlevel -302
errorlevel -305

;global labels

variable _waitknt=0

udata
regaddress res 1
databyte res 1
datachar res 1
tens_digit res 1
ones_digit res 1
convert_buffer res 1

global write_rtc,read_rtc,rtc_convert,i2c_common_setup
global regaddress, databyte, datachar, tens_digit, ones_digit, convert_buffer


;; I2C MACROS
;;
;; Sebastian K, commit 110219-2208
;; forked off PIC16 sample code
;; for PIC18F4620
;; relocatable labels



;I2C lowest layer macros;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

i2c_common_check_ack macro err_address ;If bad ACK bit received, goto err_address
btfsc SSPCON2,ACKSTAT
goto err_address
endm

i2c_common_start macro
;input: none
;output: none
;desc: initiate start conditionon the bus
bsf SSPCON2,SEN
btfss PIR1, SSPIF
bra $-2

bcf PIR1, SSPIF ;clear SSPIF interrupt bit

endm

i2c_common_stop macro
;input: none
;output: none
;desc: initiate stop condition on the bus
bsf SSPCON2,PEN
btfsc SSPCON2,PEN
bra $-2
bcf PIR1, SSPIF
endm

i2c_common_repeatedstart macro
;input: none
;output: none
;desc: initiate repeated start on the bus. Usually used for
; changing direction of SDA without STOP event
bsf SSPCON2,RSEN
btfss PIR1, SSPIF
bra $-2

bcf PIR1, SSPIF ;clear SSPIF interrupt bit

endm

i2c_common_ack macro
;input: none
;output: none
;desc: send an acknowledge to slave device
bcf SSPCON2,ACKDT
bsf SSPCON2,ACKEN
btfsc SSPCON2,ACKEN
bra $-2
endm

i2c_common_nack macro
;input: none
;output: none
;desc: send an not acknowledge to slave device

bsf SSPCON2,ACKDT
bsf SSPCON2,ACKEN

_waitl#v(_waitknt)
btfsc SSPCON2,ACKEN
goto _waitl#v(_waitknt)
_waitknt set _waitknt+1
endm

i2c_common_write macro

;input: W
;output: to slave device
;desc: writes W to SSPBUF and send to slave device. Make sure
; transmit is finished before continuing

btfsc SSPSTAT, BF
bra $-2

movwf SSPBUF

btfss PIR1, SSPIF
bra $-2
bcf PIR1, SSPIF ;clear SSPIF interrupt bit

endm

i2c_common_read macro
;input: none
;output: W
;desc: reads data from slave and saves it in W.

bsf SSPCON2,RCEN ;Begin receiving byte from
btfss PIR1, SSPIF
bra $-2
bcf PIR1, SSPIF
movf SSPBUF,w
endm
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

code

i2c_common_setup
;input: none
;output: none
;desc: sets up I2C as master device with 100kHz baud rate

movlw b'10000000'
movwf SSPSTAT ;set I2C line leves, clear all flags.

movlw 24 ;100kHz baud rate: 10000000 osc / [4*100000] -1
movwf SSPADD ;RTC only supports 100kHz

movlw b'00101000' ;Config SSP for Master Mode I2C
movwf SSPCON1

bsf SSPCON1,SSPEN ;Enable SSP module


bcf PIR2, SSPIE ;don't cause an interrupt on SSPIF, please. We're just polling it.
bcf PIR1, SSPIF
bcf SSPSTAT, BF
i2c_common_stop ;Ensure the bus is free
return

;rtc Algorithms;;;;;;

write_rtc

;input: address of register in RTC
;output: none
;Desc: handles writing data to RTC
;Select the DS1307 on the bus, in WRITE mode
i2c_common_start



movlw 0xD0 ;DS1307 address | WRITE bit
i2c_common_write
i2c_common_check_ack WR_ERR1

;Write data to I2C bus (Register Address in RTC)
movf regaddress,w ;Set register pointer in RTC
i2c_common_write ;
i2c_common_check_ack WR_ERR2

;Write data to I2C bus (Data to be placed in RTC register)
movf databyte,w ;Write data to register in RTC
i2c_common_write
i2c_common_check_ack WR_ERR3

goto WR_END

WR_ERR1
nop
movlw b'00001101'
movwf LATA

goto WR_END
WR_ERR2
nop
movlw b'00001111'
movwf LATA
bsf LATE,0
goto WR_END
WR_ERR3
nop
movlw b'00001001'
movwf LATA
goto WR_END
WR_END
i2c_common_stop ;Release the I2C bus
return

;; ************************************************** READ RTC
read_rtc
;input: address of RTC
;output: DOUT or 0x75
;Desc: This reads from the selected address of the RTC
; and saves it into DOUT or address 0x75

;Select the DS1307 on the bus, in WRITE mode

i2c_common_start

movlw 0xD0 ;DS1307 address | WRITE bit
i2c_common_write ;
i2c_common_check_ack RD_ERR1

;Write data to I2C bus (Register Address in RTC)
movf regaddress,w ;Set register pointer in RTC
i2c_common_write ;
i2c_common_check_ack RD_ERR2

;Re-Select the DS1307 on the bus, in READ mode
i2c_common_repeatedstart
movlw 0xD1 ;DS1307 address | READ bit
i2c_common_write
i2c_common_check_ack RD_ERR3

;Read data from I2C bus (Contents of Register in RTC)
i2c_common_read
movwf datachar
i2c_common_nack ;Send acknowledgement of data reception


goto RD_END

RD_ERR1
nop
movlw b'00000011'
movwf LATA
goto RD_END
RD_ERR2
nop
movlw b'00000101'
movwf LATA
goto RD_END
RD_ERR3
nop
movlw b'00000111'
movwf LATA
goto RD_END
;Release the I2C bus
RD_END
i2c_common_stop
return

rtc_convert
;input: W
;output: tens_digit, ones_digit
;desc: This subroutine converts the binary number
; in W into a two digit ASCII number and place
; each digit into the corresponding registers
; dig10 or dig1

movwf convert_buffer ; B1 = HHHH LLLL
swapf convert_buffer,w ; W = LLLL HHHH
andlw 0x0f ; Mask upper four bits 0000 HHHH
addlw 0x30 ; convert to ASCII
movwf tens_digit ;saves into 10ths digit

movf convert_buffer,w
andlw 0x0f ; w = 0000 LLLL
addlw 0x30 ; convert to ASCII
movwf ones_digit ; saves into 1s digit
return



end

rtc_macros.inc

;External labels
extern write_rtc,read_rtc,rtc_convert,i2c_common_setup, regaddress, databyte, datachar

;; RTC MACROS
;;
;; Sebastian K, commit 110219-2205
;; forked off PIC16 sample code
;; for PIC18F4620
;; relocatable labels, declared in another file

variable _loopknt=0

rtc_resetAll macro
;input: none
;output: none
;desc: Resets all the time keeping registers on the RTC to zero


clrf databyte
movlw 6
movwf regaddress ;start at 6 and go down, and set all to 0

del_loop#v(_loopknt)
call write_rtc
decfsz regaddress
bra del_loop#v(_loopknt)
call write_rtc ;sets registers 0-6 to zero
_loopknt set _loopknt+1
endm




rtc_set macro addliteral,datliteral
;input: addliteral: value of address
; datliteral: value of data
;output: none
;desc: loads the data in datliteral into the
; address specified by addliteral in the RTC

movlw addliteral
movwf regaddress
movlw datliteral
movwf databyte
call write_rtc
endm

rtc_read macro addliteral
;input: addliteral
;output: datachar, tens_digit, ones_digit
;desc: From the selected register in the RTC, read the data
; and load it into 0x75. 0x75 is also converted into
; ASCII characters and the tens digit is placed into
; 0x77 and the ones digit is placed in 0x78
movlw addliteral
movwf regaddress
call read_rtc
movf datachar,w
call rtc_convert
endm