It has been brought to my attention that the previous message I sent
was not readable.  I have fixed this problem and want to say I am
sorry for the previous message.

I am trying to use a maxum 7219 serial display chip with a pic
16c74a.  I have the serial port working correctly on the pic but the
maxim chip is still not displaying anything.  The pic is running
with a 4 MHz crystal.

If you can see a problem with this program please let me know, or if
you have a working routine for this maxim chip please send it my way.

thank you

********Program currently set to display 1 digit************

;this is the pic and display information needed to init the
;Serial port and the multiplexing chip.
;
;
;init these values
        LIST  P=16C74A, F=INHX8M
        include <p16c74a.inc>


        ORG     0x00                                              ;reset program
 position
        GOTO    START                                      ;go to the start of
 the program

;init serial port
START
        clrf    PORTA
        movlw   0x00
        tris    PORTA

        clrf    PORTB           ;portb is used to pulse a line so that
        movlw   0x00            ;there is a point we can check to see that
        tris    PORTB           ;the pic program is running

        clrf    PORTC           ;clears port
        movlw   0x00            ;sets i/o pins to proper values
        tris    PORTC           ;port is now set for only outputs
                                ;because we are not going to receive data
                                ;only 5 pins are required at this point these
                                ;are pins 18, 23, 24, 25, 26


        movlw   0x00            ;set proper bits for spi operation
        bsf     STATUS, RP0     ;switch to bank 1
        movwf   SSPSTAT         ;
        bcf     STATUS, RP0     ;switch to bank 0
        movlw   0x21            ;pic is set as master with
        movwf   SSPCON          ;a 1/4 the fosc
        bsf     PORTC, 6

;test porgram
repeat
        movlw   0x0c            ;Set to normal operation
        call    SEND
        movlw   0x01            ;take maxium chip out of shutdown
        call    SEND
        bcf     PORTC, 6                           ;pulse load line to latch 16
bits
        nop
        nop
        nop
        bsf     PORTC, 6


        movlw   0x09            ;declare decode mode b
        call    SEND
        movlw   0xff            ;Set all digits to decode B
        call    SEND
        bcf     PORTC, 6        ;latch data
        nop
        nop
        nop
        bsf     PORTC, 6

        movlw   0x0a            ;init intensity
        call    SEND
        movlw   0x0f            ;intensity set to max
        call    SEND
        bcf     PORTC, 6                          ;latch data
        nop
        nop
        nop
        bsf     PORTC, 6

        bcf     PORTB, 1        ;set a bit on port b high
                                ;to confirm this point has
                                ;been reached

        movlw   0x0b            ;init scan limit
        call    SEND
        movlw   0x00            ;only one digit is being displayed so far
        call    SEND            ;other digits will be added once 1 display is
        bcf     PORTC, 6                           ;working
        nop
        nop
        nop
        bsf     PORTC, 6

        movlw   0x0f            ;turn display test off
        call    SEND
        movlw   0x00            ;takes maxium chip out of test mode
        call    SEND
        bcf     PORTC, 6
        nop
        nop
        nop
        bsf     PORTC, 6


        movlw   0x01            ;send data to digit
        call    SEND
        movlw   0x01            ;this should display the digit 1
        call    SEND
        bcf     PORTC, 6
        nop
        nop
        nop
        bsf     PORTC, 6

        bsf     PORTB, 1                           ;set pin on port b high to co
nfirm
                                ;porgram finished

        goto    repeat          ;repeat program


;send subroutine
SEND    movwf   SSPBUF          ;move data to transmit to proper register
        bsf     STATUS, RP0     ;switch to bank 1
LOOP    btfss   SSPSTAT, BF     ;has final bit been sent
        goto    LOOP            ;if not loop
        bcf     STATUS, RP0     ;switch to bank 0
        movf    SSPBUF, W
        return
;
        end

Brian Ward
Send all comments to:
Wardbria@mailserv1.ferris.edu