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 handshaking. Before this routine is called the LISTEN routine, FFB1, must be used to command a device on the serial bus to get ready to receive data. the accumulator is loaded with a byte to output 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. So when a call to the UNLISTEN routine, FFAE, is made to end the data transmission, the buffered character is sent with EOI set. Then the UNLISTEN command is sent to the device.