Commodore Plus 4 - Page 324

312 Machine Language on the Commodore Plus/4
$03 = The specified logical file is not open.
$05 = The specified device is not present.
$07 = The specified device is not an output device.
The system I/O status byte may also be checked for errors. It is read using
READSS ($FFB7).
SFFCC CLRCH
Registers Altered: .A, .X
This routine is vectored through $0320-$0321. The input and output channels
are cleared. If the serial bus or DMA disk was in use, an unlisten or untalk
command is sent. The input and output devices are reset to the keyboard and
screen.
The system I/O status byte may be checked for errors. It is read using
READSS ($FFB7).
$FFCF BASIN
Registers Altered: .A
This routine is vectored through $0322-$0323. This subroutine returns 1 byte
in .A from the current input channel. For all devices except the keyboard, calls to
OPEN ($FFC0) and CHKIN ($FFC6) must precede this call. The channel
remains open following the call to this routine.
The system I/O status byte may be checked for errors. It is read using
READSS ($FFB7).
For the keyboard, the first call to this routine turns on the cursor at its current
location and receives input (including function key definitions) that is echoed to
the screen until a carriage return is detected. A full screen of characters may be
entered. When the carriage return is received, the routine returns with the first
character in .A. Each subsequent call returns the next character. The input is
complete when a carriage return ($0D) is returned.
SFFD2 BSOUT
Registers Altered: none*
This routine is vectored through $0324-$0325. The byte in .A is sent to the
output channel. For all devices except the screen, calls to OPEN ($FFC0) and
CHOUT ($FFC9) must precede this call. The channel remains open following a
call to this routine.
The system I/O status byte may be checked for errors. It is read using
READSS ($FFB7).
♦When used to send data to device 1 (the cassette) or 2 (RS-232), this routine may alter the value
of .A on return.