Commodore Amiga A500 Technical Reference Manual page 75

BUGS
SYSTEWLIBRARIESI
NAME
EXPANSION1
READEXPANS~ONBYTE
ReadExpansionByte
-
read a byte nybble by nybble.
SYNOPSIS
byte
=
ReadExpansionByte( board, offset
)
DO A0 DO
FUNCTION
ReadExpansionByte reads a byte from a new-style expansion board.
These boards have their readable data organized as a series of
nybbles in memory. This routine reads two nybbles and returns the
byte value.
In general, this routine will only be called by ReadExpansionRom.
The offset is a byte offset into a ExpansionRom structure. The actual
memory address read will be four times larger. The macros
EROFFSET and ECOFFSET are provided to help get these offsets
from C.
INPUTS
board
-
a pointer to the base of a new style expansion board. offset
-
a logical offset from the board base
RESULTS
byte
-
a byte of data from the expansion board, or
-1
if there was
an error reading from the board.
EXAMPLES
byte
=
ReadExpansionByte( cd->BoardAddr, EROFFSET( er-Type
)
);
ints
=
ReadExpansionByte( cd->BoardAddr, ECOFFSET
(
ec-Interrupt
) );
EXCEPTIONS
SEE ALSO
WriteExpansionByte, ReadExpansionRom
BUGS