DMX on 250000 baud receive

[DynamoBen]

Like most things there is more than one way to accomplish a task. Last year I saw the post from JEC about DMX. While it was nice to hear that DMX was possible with PICBasic I really wanted something that was interrupt based.

After doing some research I found that all you need to do is look for a framing error, after which should be the start code (there may be several framing errors in a row). Over the last few days I have created the interrupt code snip below. While I haven't tested it exhaustively it seems to work.

DimmerCount	VAR WORD  ; Location in DMX string
DMXStartAddr	VAR WORD  ; DMX start address
DMXStartCode	VAR BYTE  ; DMX Start code (Dimmer=0)
Dummy		VAR BYTE
DMX_State	VAR BYTE  ; Stage of DMX reception     

Valid_Break     CON 1
Valid_SC        CON 2
Valid_Data     CON 3

Disable

INTERRUPT_SUB:
	IF OERR Then 						
		CREN = 0
		CREN = 1    			; Clear Overrun Errors
		High Err_LED			; Notify user of overrun error
		DMX_State=0
		EndIF

	IF FERR Then
        	FERR = 0
		DMX_State=Valid_Break
	Else
		GoSub RX_DMX_Data							
     	EndIF
     	
    	Dummy=RCREG				; Empty UART of junk data
	Resume	

RX_DMX_Data: 
	IF DMX_State=Valid_Break Then
		HSerin 20,NoData,[DMXStartCode]	; Start code of 0 = dimmer data
		
		IF DMXStartCode=0 Then 
			DMX_State=Valid_SC
		Else
			High Err_LED		; Notify user of Error in Start Code
			DMX_State=0 
			EndIF
		EndIF
		
	IF DMX_State=Valid_SC Then
		For DimmerCount=0 TO DMXStartAddr; Count incoming data bytes (frames) 
			Dummy=RCREG		; Read unwanted values
			Next DimmerCount
		DMX_State=Valid_Data
		EndIF
		
	IF DMX_State=Valid_Data Then
		HSerin 20,NoData,[STR DataBuffer\Number_Of_Channels]
		DMX_State=0
		EndIF
		
	IF DMX_State=0 Then
		Resume
		EndIF
	
GoTo RX_DMX_Data
	
NoData:
	DMX_State=0
	Resume
		
Enable
End