Thanks, that was very helpful. I now have a a working text console. Woot!

One unexpected thing when I started was that the terminal window needed to have the baud configured. Yeah, I should have expected full serial emulation for MAME smile I was able to fix it partly with this:

DEVICE_INPUT_DEFAULTS_START( terminal )
DEVICE_INPUT_DEFAULTS( "RS232_RXBAUD", 0xff, RS232_BAUD_38400)
DEVICE_INPUT_DEFAULTS( "RS232_TXBAUD", 0xff, RS232_BAUD_38400)
DEVICE_INPUT_DEFAULTS( "RS232_DATABITS", 0xff, RS232_DATABITS_8 )
DEVICE_INPUT_DEFAULTS( "RS232_PARITY", 0xff, RS232_PARITY_NONE )
DEVICE_INPUT_DEFAULTS( "RS232_STOPBITS", 0xff, RS232_STOPBITS_1 )
DEVICE_INPUT_DEFAULTS_END


It looks like this worked, but the 2681's Rx seems to be stuck at 9600, so terminal input is garbled. It's possible my 2681 code is only configuring the Tx baud rate, but this works on real hardware at 38.4k. I vaguely recall the real hardware has automatic rate detection. Maybe that's different here. More debugging...