MC68HC812A4 Datasheet, PDF (94/342 Pages) Motorola, Inc – 16-bit device composed of standard on-chip peripheral modules connected by an intermodule bus. Modules include

Bus Control and Input/Output (I/O)
6.3 Detecting Access Type from External Signals
The external signals LSTRB, R/W, and A0 can be used to determine the
type of bus access that is taking place. Accesses to the internal RAM
module are the only type of access that produce LSTRB = A0 = 1,
because the internal RAM is specifically designed to allow misaligned
16-bit accesses in a single cycle. In these cases, the data for the
address that was accessed is on the low half of the data bus and the data
for address +1 is on the high half of the data bus.
Table 6-1. Access Type versus Bus Control Pins
LSTRB
A0
R/W
1
0
1
0
1
1
1
0
0
0
1
0
0
0
1
1
1
1
0
0
0
1
1
0
Type of Access
8-bit read of an even address
8-bit read of an odd address
8-bit write of an even address
8-bit write of an odd address
16-bit read of an even address
16-bit read of an odd address
(low/high data swapped)
16-bit write to an even address
16-bit write to an even address
(low/high data swapped)
MC68HC812A4 — Rev. 3.0
94
Bus Control and Input/Output (I/O)
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