Commodore Plus 4 - Page 320

308 Machine Language on the Commodore Plus/4
SFF9C MEMBOT
Registers Altered: .X, .Y
When called with the carry set, returns with .X equal to the low byte of the
bottom of memory, and. Y equal to the high byte of the bottom of memory. When
called with the carry clear, the bottom of memory ($0531-$0532) is set. The low
byte is from .X and the high byte from . Y. Only the high byte of the bottom of
memory is initialized during the power-on sequence. BASIC does not use this
information.
$FF9F SCNKEY
Registers Altered: .A, .X, .Y
Scans the keyboard and sets up the keyboard queue and the function key index
register for the GETIN ($FFE4) and BASIN ($FFCF) routines. This subroutine
is normally called by the system IRQ service routine.
SFFA2 SETTMO
Registers Altered: none
The value in .A is stored in the timeout flag ($0535). This location is not used by
the built-in Plus/4 operating system. It is designed for use with add-on hardware
and software.
SFFA5 ACPTR
Registers Altered: .A
Returns 1 byte of data in .A from the serial bus or DMA disk using handshak
ing. A device must be instructed to talk using the routine TALK ($FFB4) before
this routine is called.
The system I/O status byte may be checked for errors. It is read using
READSS ($FFB7).
SFFA8 CIOUT
Registers Altered: none
Sends the byte in .A to the serial bus or DMA disk using handshaking.
Normally, one or more devices will have been instructed to listen using the
routine LISTN ($FFB1) before this routine is called.
The system I/O status byte may be checked for errors. It is read using
READSS ($FFB7).