My brain is fried, so I thought I would pass this one to the community.

When sending 1 character to my embedded system, it consistently thinks it receives 2 characters. The first received character seems to map to the transmitted character (in some unkown way) and the second received character is always 0xff

Here is what I observed:

Tx char (in hex)    Rx character (in hex), I left out the second byte (always ff)
31                    9D
32                    9B
33                    99
61                    3D
62                    3B
63                    39
64                    37
65                    35
41                    7D
42                    7B
43                    79

I have check my clocks and them seem to be ok. The only diff between this non working version and the previous version is that i am now using a RS485 chip. I have traced the signal all the way up to the MCU and it looks fine (confirmed the bit value on the rx pin)