Commodore Plus 4 - Page 321

The Operating System 309
SFFAB UNTLK
Registers Altered: .A
Commands all devices on the serial bus or the DMA disk to stop talking (see
TALK, $FFB4).
The system I/O status byte may be checked for errors. It is read using
READSS ($FFB7).
$FFAE UNLSN
Registers Altered: .A
Commands all devices on the serial bus or the DMA disk to stop listening (see
LISTN, $FFB1).
The system I/O status byte may be checked for errors. It is read using
READSS ($FFB7).
$FFB1 LISTN
Registers Altered: .A
Commands a device on the serial bus or the DMA disk to listen. The device
number ($04-$ IF) must be in .A. Also, if it has not previously been set, the device
number must be stored in the current device number ($AE) before this routine is
called.
The system I/O status byte may be checked for errors. It is read using
READSS ($FFB7).
SFFB4 TALK
Registers Altered: .A
Commands a device on the serial bus or the DMA disk to talk. The device
number ($04-$ 1F) must be in .A. Also, if it has not previously been set, the device
number must be stored in the current device number ($AE) before this routine is
called.
The system I/O status byte may be checked for errors. It is read using
READSS ($FFB7).
$FFB7 READSS
Registers Altered: .A
Returns the current value of the I/O status byte ($90) in .A. The bits of the
status byte have various meanings depending on the device accessed. In general, a
value of zero indicates no error. Some of the meanings of the status bits are
outlined in the following table.