RX / TX duo

[mbw123]

Sorry Bruce, my browser freaked out for a second and I didn't scroll down to see the rest of your post. Thanks for the help!!

-Mike

[skimask]

Nothing wrong with your schematic. Same basic design I use. As far as manchester code...roll your own. You wouldn't like what I'm using, kludged up, works for me, but it's ugly.
JDG

[Bruce]

I rarely use manchester, but here's a simple version you can run with a
terminal program to see how it works. You can easily change it to work
with serial comms between two PIC via RF.

You still want to include a preamble & synch byte before each packet.

The assembler routine is a slightly modified version of one done by Les
Johnson a long time ago, and it's very fast.

This version is for an 18F. Just make the rotate instruction change as shown
to use it on a 12F or 16F part. You'll want to change banka to bank0 also.

; Compile with MPASMWIN
X           VAR BYTE
Y           VAR BYTE
BitCount    VAR BYTE banka system ' Bank0 system so we don't need an underscore
ByteIn      VAR BYTE banka system ' to access BASIC variables from assembler
ByteOut     VAR BYTE banka system
Manch       VAR WORD banka system ' Holds manchester encoded word
Temp        VAR WORD banka system ' Temp var
CRC         VAR BYTE system
Enc_Dat     VAR WORD[6]           ' Holds 6 manchester encoded words
    
    GOTO Main   ' Jump over encode/decode routines
    
ASM  ; Note: For 14-bit core just change Rlcf to Rlf
     ; Manchester encode routine
_Encode
	Movlw   8
	Movwf   BitCount
E_Repeat
	Rlcf    ByteIn,F   
	Btfss   STATUS,C
	Goto    BitClr     
BitSet                 
	Rlcf    Manch,F
	Rlcf    Manch+1,F
	bcf     STATUS,C
	Rlcf    Manch,F
	Rlcf    Manch+1,F
	Goto    E_Loop
BitClr                 
	Rlcf    Manch,F
	Rlcf    Manch+1,F
	bsf     STATUS,C
	Rlcf    Manch,F
	Rlcf    Manch+1,F
E_Loop
	Decfsz  BitCount,F
	Goto    E_Repeat
	Return
ENDASM
    
ASM
    ; Manchester decode routine.
_Decode
	Movf    Manch+1,W
	Movwf   Temp+1
	Movf    Manch,W
	Movwf   Temp
	Movlw   8
	Movwf   BitCount
Repeat
	Rlcf    Temp,F       
	Rlcf    Temp+1,F  
	Rlcf    ByteOut,F  
	Rlcf    Temp,F      
	Rlcf    Temp+1,F   
	Decfsz  BitCount,F
	Goto    Repeat
	Return
ENDASM
	
Main:
    ' Manchester encode ASCII characters "A" to "F"
    Y = 0       ' Start array index pointer at 0
    FOR X = "A" to "F"
     ByteIn = X
     CALL Encode
     Enc_Dat[Y] = Manch
     HSEROUT ["Encoded ",X," = ",IBIN8 X," = ",IBIN16 Enc_Dat[Y],13,10]
     Y = Y + 1  ' Increment array index pointer
    NEXT X
    
    ' Decode & print results
    FOR Y = 0 to 5
     Manch = Enc_Dat[Y]
     CALL Decode
     HSEROUT ["Decoded ",IBIN16 Manch," = ",ByteOut,13,10]
    NEXT Y
    PAUSE 10000
    GOTO Main
    
    END

Here's the output;

Encoded A = %01000001 = %0110010101010110
Encoded B = %01000010 = %0110010101011001
Encoded C = %01000011 = %0110010101011010
Encoded D = %01000100 = %0110010101100101
Encoded E = %01000101 = %0110010101100110
Encoded F = %01000110 = %0110010101101001
Decoded %0110010101010110 = A
Decoded %0110010101011001 = B
Decoded %0110010101011010 = C
Decoded %0110010101100101 = D
Decoded %0110010101100110 = E
Decoded %0110010101101001 = F

Manchester does have its advantages, but I rarely use it. A big factor is
getting the receiver/transmitter in synch.

Like in my previous post, I would definitely use a preamble followed by a
synch character. That really makes a big difference.

[skimask]

I was doing some reading awhile back on these various modules using On/Off keying, FSK/ASK, whatever. I can see the modules working fine when only sending small data packets that only end up lasting a few milliseconds (with a good preamble of course). But, from what I've read, it seems that the data slicer will lose it's mind after that especially if the data has a lot of repeating 0's or 1's.
Correct or wrong?
JDG

[Bruce]

Long periods of 0's will cause problems.

Short bursts of information like preamble,synch,address,data,checksum etc
work just fine. The payload is delivered just after everything is stable and in
synch. Even a few bytes of data with large numbers of 0's works, but you
wouldn't want to stuff 50 words in there made up of all 0's.

If you're transmitting long streams of serial data that can vary from all 0's
to all 1's, then you might want to look into using manchester.

Here's one example of how a simple remote control encoder works.
http://www.linxtechnologies.com/docu...datastruct.pdf

[mbw123]

Bruce,
I didn't read your first post carefully enough. In your receiver code you had the SERIN line say:

SERIN2 D_IN,BAUD,[WAIT(Synch),ADD_IN1,DAT_IN1,ADD_IN2...]

What does the WAIT(Synch) line do?

I appreciate your answering, as this is probably a stupid question.

Thanks!!

-Mike

[Bruce]

It WAITs for the Synch byte. Look in your PBP manual under SERIN2 for the
WAIT modifier. This forces the SERIN2 line to wait until this specific byte
arrives before receiving the rest of the serial packet.