Alexander:

Thanks for the response. It prompted me to do a lot of reading.

Showing my age, parity was always the MSB of an 8-bit byte. There also appears to be an unfortunate reuse of the term "parity". In some implementations of RS-485 systems, the 9th "parity" bit is used to key the end nodes that the current byte is an address(see MAX 3140 datasheet). This allows the end node to quickly determine if the message is for it without having to decode the packet.

This 9th bit is generated internally by the UART based on the value of the parity bit. So, which parity bit is the Perl modules dealing with? And do the modules allow this definition to be changed at will to drive the address function out onto the RS-485 bus?

Interesting topic.

James