Hi Folks,

we have note made a DMX-512 receiver but as the topic is under discussion:
I have included a parallel to DMX-512 converter code for PIC running at 4MHz
which I wrote as a tool to test DMX-512 receivers (what I never have...)

well maybe it is useful to someone

antti

;            Parallel to DMX-512 Converter
; Copyright (C) 1996 Silicon Studio. All rights reserved.
;
; Target PIC16C5X or PIC16CXX at 4MHz Clock
;
; Description of hardware:
; Port B 8 Bit Data Input
; RA0 DMX-512 Output
; RA1 Busy/Ready Output
; RA2 Strobe Input
;
; This device will set Ready and wait for Strobe
; and transmit 8 bit data at 250 kbaud! that all it does!
; It should be possible to use it connected
; to LPT as demo device for testing DMX-512 system?
; (We have not done it)
; comments as always to comment@sistudio.com :)_
;
 Processor 16CXX                ;Select correct type?
 __FUSES 0x3FF9

dmx_port = 5                    ;Port A
host_port = 5
data_port = 6                   ;Port B

tx_reg   = 0x0f                 ;Transmit register

#define busy_out host_port,1    ;Busy output
#define strobe_in host_port,2   ;Strobe input

#define w_ready movlw 0x03      ;TX out inactive, not Busy
#define w_busy andlw 0xFD       ;Set busy in W, tricky here...

;
; Start
;
        movlw 0x01              ; Not Ready, TX out inactive
        movwf host_port         ; Set outputs
        movlw 0xFC              ; PA0, PA1 are outputs
        tris host_port          ; Set TRIS

loop    w_ready                 ;4
        movwf host_port         ;4 STOP is generated here

wait_strobe
        btfss strobe_in         ; Strobe?
        goto wait_strobe        ; Wait for HOST Strobe
;
; 250 KBaud Async Serial Transmitter
;
        bcf     dmx_port,0      ;4      ->Start

        movwf   tx_reg          ;4
        movf    tx_reg,W        ;4
        w_busy                  ;4
        movwf   dmx_port        ;4      ->0

        rrf     tx_reg,F        ;4
        movf    tx_reg,W        ;4
        w_busy                  ;4
        movwf   dmx_port        ;4      ->1

        rrf     tx_reg,F        ;4
        movf    tx_reg,W        ;4
        w_busy                  ;4
        movwf   dmx_port        ;4      ->2

        rrf     tx_reg,F        ;4
        movf    tx_reg,W        ;4
        w_busy                  ;4
        movwf   dmx_port        ;4      ->3

        rrf     tx_reg,F        ;4
        movf    tx_reg,W        ;4
        w_busy                  ;4
        movwf   dmx_port        ;4      ->4

        rrf     tx_reg,F        ;4
        movf    tx_reg,W        ;4
        w_busy                  ;4
        movwf   dmx_port        ;4      ->5

        rrf     tx_reg,F        ;4
        movf    tx_reg,W        ;4
        w_busy                  ;4
        movwf   dmx_port        ;4      ->6

        rrf     tx_reg,F        ;4
        movf    tx_reg,W        ;4
        w_busy                  ;4
        movwf   dmx_port        ;4      ->7

        goto    loop            ;8

        END

;

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-- http://www.sistudio.com