This routine is used to send information to devices on the serial bus. A call to this routine will put a data byte onto the serial bus using full serial handshaking.

Before this routine is called, the LISTEN routine must be used to command a device on the serial bus to get ready to receive data. If a device needs a secondary address, it must also be sent by using the SECOND routine.

The accumulator is loaded with a byte to handshake as data on the serial bus. A device must be listening or the status word will return a timeout.

This routine always buffers one character. (The routine holds the previous character to be sent back.) So when a call to the UNLSN routine is made to end the data transmission, the buffered character is sent with an End Or Identify (EOI) set. Then the UNLSN command is sent to the device.