Hi Trend, had you any success with your project to connect a MDB bill acceptor to a PIC?
I'm running in the same situation and I think the additional bit after the 8th data bit could be a problem because IT IS NOT a parity bit. It is a basically a flag.

For who wish to help on that, I'll report what the official documentation said about the MDB protocol:
Baud rate: 9600 NRZ
Serial bit format:
1 start bit
8 data bits
1 MODE BIT
1 stop bit
Total: 11 bits

MODE BIT: Master-To-Peripheral
"The Mode bit differentiates between ADDRESS bytes and DATA bytes. ADDRESS bytes must be read by all peripherals, DATA bytes are only read by the peripheral that has been addressed".
"The MODE BIT is set (logic one) to indicate an ADDRESS byte, and not set (logic zero) to indicate a DATA byte".

MODE BIT: Peripheral-To-Master
"The MODE bit must be set on the last byte sent when data is sent from a Slave to the Master".

Any idea?
Thank you a lot.