RS485 Basic Test

[Mr. Duke]

I am trying to do very basic RS485 communication and I am having very frustrating results. I have read many of the forum posts regarding RS485 and still don't really know how to explain my results.

I am using a MAX485 chip. I can reliable send a byte 0x30 and on the receiving end I see 0x98. The PIC chip is sending data to a PC with a USB/RS485 device using HTerm. I can connect the same computer to another device communicating over RS485 sending a known data stream and it appears on the PC as expected. This leads me to believe the problem exists with whatever I am doing on the PIC chip.

Any help is appreciated. Code snippet below.

#chip 16F628A, 4
#config OSC = INTOSC
#option Explicit

#define USART_BAUD_RATE 9600
#define USART_BLOCKING
#define SerInPort PORTB.1
#define SerOutPort PORTB.2
#define masterslave PORTB.0

Dir SerInPort In
Dir SerOutPort Out
Dir masterslave Out

START:
'Start RS485 Code
DATA:
'Send some data
Set masterslave ON
HSerSend 0x30
wait 2 ms
Set masterslave OFF
End

[Mr. Duke]

I actually figured out my own problem. I'm embarrassed to admit that in my haste to create a quick circuit I had failed to place any filter capacitors on my power supply. That seemed to be causing my issues. Everything is working as expected now.