MC68HC812A4 Datasheet, PDF (106/342 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)
LSTRE — Low Strobe (LSTRB) Enable Bit
Normal modes: Write once
Special modes: Write anytime except the first time
LSTRE has no effect in single-chip or normal expanded narrow
modes.
1 = PE3 is configured as the LSTRB bus-control output, except in
single-chip or normal expanded narrow modes.
0 = PE3 is a general-purpose I/O pin.
LSTRB is for external writes. After reset in normal expanded mode,
LSTRB is disabled. If needed, it must be enabled before external
writes. External reads do not normally need LSTRB because all 16
data bits can be driven even if the MCU only needs eight bits of data.
In normal expanded narrow mode, this pin is reset to an output driving
high allowing the pin to be an output while in and immediately after
reset.
RDWE — Read/Write Enable Bit
Normal modes: Write once
Special modes: Write anytime except the first time
RDWE has no effect in single-chip modes.
1 = PE2 is configured as the R/W pin. In single-chip modes, RDWE
has no effect and PE2 is a general-purpose I/O pin.
0 = PE2 is a general-purpose I/O pin.
R/W is used for external writes. After reset in normal expanded mode,
it is disabled. If needed, it must be enabled before any external writes.
MC68HC812A4 — Rev. 3.0
106
Bus Control and Input/Output (I/O)
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