Solution:

Here is a comment from the Engineers about using 9 bit with our converters. 9 bit protocol is a simple master/slave protocol. The master uses 9 bit messages (playing games with the parity bit) to indicate to the slaves that it’s an addressing command so they all need to pay attention to see if it’s addressed to them, then it reverts to 8 bit to send the data and all the other slaves can ignore the traffic. It’s had niche use for a few decades. Correct that a windows device (PCI or USB to serial) would choke on this 8/9 bit flipping unless the driver had a special provision for it. However, any B&B serial-serial product is fine with it; the only issue is the byte length varies by 1 bit width depending on if it’s an address or data byte. Invisible to any of our bit-wise SDC circuits, but our byte-time circuits may need a slightly longer timeout as some of the bytes will appear to be 10% “slower” than the actual baud rate. If that doesn’t correct the problem, then something else is going on, likely unrelated to the 9 bit issue.