Function Name: LISTEN

Purpose: Serial - send listen command
Call address: $FFB1 (hex) 65457 (decimal)
Preparation:

	Registers:	.A = device (0-31)
	Memory:		system map
	Flags:		none
	Calls:		none

	Registers:	.A used
	Memory:		STATUS ($90)
	Flags:		none

Description: LISTEN is a low-level Kernal serial bus routine that sends a LISTEN command to the serial bus device in .A. It commands the device to start reading data. (Most applications should use the higher-level I/O routines; see CHKOUT.)

EXAMPLE:

	JSR	$FFB1	;command device to LISTEN