I've been looking at the null_modem setup for RS232, to implement a device for the MPU4 and similar drivers, namely the BACTA datalogger. It's a specification part, where the key to handling communication is to run as a null modem at 1200 baud, 1 start bit, 8 databits, odd parity and 1 stop bit.
I had intended to fork the null modem implementation that already exists in bus/rs232, as there are only two real differences. 1 is that the data frame configuration is fixed, and the other is that when a receive operation is complete, the character is logged for later recall and 0x06 is sent back as the acknowledgement response.
My question is, effectively, what is the most MAME appropriate way of doing this? As I say, the connection is standard RS232, so I want to represent that up to a point, but it's not really appropriate as a full on RS232 device as its scope is so limited.