Pair of PICs, Xbee's and rs232

[Michael]

here's what's happening (or not happening) -- doesn't make sense.

transmit:
PICserout rs232 > sn75276 convert to rs485 > another sn76176 back to rs232 > XBEE datain > rf out

receive:
rf in > XBEE dataout > sn75176 convert to rs485 > another sn75176 back to rs232 > PICserinrs232

The above works like a champ. Only 1200 baud and it transmits a good 150'. (No doubt your wondering about the two sn75176 -- seems redundant but no time to explain).

If I simply remove the sn75176b chips and don't change ANYTHING -- in other words, a direct rs232 connection -- it won't function.

I have proper 3.3v to 5v level conversion everywhere, I've tried pullups and pulldowns, a series resistor and nothing.

I do see a data stream on my scope at the receiver end but it cuts in and out. ??? !

[amgen]

how about 232 transmit from pic inverted, xbee probably looking for correct polarity of 232. send and recieve on pics.

[Michael]

you beat me to it -- funny because i tried a chip inversion to try and fix it but no go -- then I tried T1200 (was using N1200).

the xbee must need true? changed both the rcvr and xmtr to T1200 and they work fine -- which tells me the sn75176 must invert as well.

[amgen]

ok, why the 2 485 chips each and don't you want to go to higher baud like 38k or more ?

[Michael]

Simple I/O Industrial control -- opto isolated and 1200 baud for reliability -- the rs485 chips are there because the PCB will retrofit into another product.