Xmit Serial RS232 from 18X to APRS device

I am trying to Serout a 48+ Hex character string from my 18X to another PIC device that is performing a format change ( my PIC weather data to a Byonics WXtrak APRS PIC modem)
I can send the appropriate WX format string from my PC using a TeraTerm terminal program to the WXtrak unit and it receives the data OK and formats it into APRS data and xmits OK

When I construct the same data string in my 18X and send to my PC , TeraTerm displays it OK....BUT when I send the same string to the WXtrak unit it does not receive/format it

With my PC connection to the WXtrak I have ALL RS232 pins connected, but with the 18X I am using only the out5 pin + ground.......again this works OK from the 18X to the PC

With my 18X I am sending the following string every 2 secs and WXtrak tries to format/tx it every 20 secs

Serout 5, N2400, ("!!+48HEX characters",13,10)

Have tried with both CR,LF (13,10) and without

The WXTrak unit has a "data valid" LED that comes on when I send my PC data but very infrequently flashes with my 18X data

Are there any "hidden " characters that the 18X is sending that WXtrak can't verify OR is it possible that there is a timing issue between the 18X and the WXtrak chip (internal resonator vs external resonator) ????

Should I construct my data in the 18X registers and xmit as b1,b2,b3, etc ????

Anyone have any experience trying this or any suggestions to what I can try

floman said:

With my PC connection to the WXtrak I have ALL RS232 pins connected, but with the 18X I am using only the out5 pin + ground.......again this works OK from the 18X to the PC

Click to expand...

Your question is well written. We should be able to get to the bottom of this quite quickly.

The 18X should not be sending any extra characters so there are only two possibilities:

1. The timing is out, hence play around with the calibfreq command

2. The WXtrack needs more than the RX pin and GND connected.


I would guess that the WXtrack only needs the RX and Gnd connected. But you should check the circuit diagram just to be sure. If the diagram is not clear, you can always connect the computer to the WXtrack with just two wires and see if everything works then.

If it does, you need to play with the calibfreq command. Try these figures first -1, -2, 1, 2, then try bigger numbers.

The last batch of 28X1 chips I got had to be set to calibfreq -4 for them to work with my overclocked 08M. But I have found the 18X range to be pretty good.

My experience is that serout and serin are pretty sensitive to the calibfreq command.

Haxby...........thanks for the advice
I used the calibfreq command and got everthing to work properly