M38002M4 Datasheet, PDF (123/173 Pages) Mitsubishi Electric Semiconductor – 8-BIT SINGLE-CHIP MICROCOMPUTER

APPENDIX
3.3 Notes on use
3.3.5 Notes on memory expansion mode and microprocessor mode
(1) Writing data to the port latch of port P3
In the memory expansion or the microprocessor mode, ports P30 and P31 can be used as the output port. Use the
LDM or STA instruction for writing data to the port latch (address 000616) of port P3.
When using a read-modify-write instruction (the SEB or the CLB instruction), allocate the read and the write
enabled memory at address 000616.
Reason
In the memory expansion or microprocessor mode, address 000616 is allocated in the external area.
Accordingly,
L Data is read from the external memory.
L Data is written to both the port latch of the port P3 and the external memory.
Accordingly, when executing a read-modify-write instruction for address 000616, external memory data is read and
modified, and the result is written in both the port latch of the port P3 and the external memory. If the read enabled
memory is not allocated at address 000616, the read data is undefined. The undefined data is modified and written
to the port latch of the port P3. The port latch data of port P3 becomes “undefined.”
(2) Overlap of an internal memory and an external memory
When the internal and the external memory are overlapped in the memory expansion mode, the internal memory
is valid in this overlapped area. When the CPU writes or reads to this area, the following is performed :
L When reading data
Only the data in the internal memory is read into the CPU and the data in the external memory is not read into
the CPU. However, as the read signal and address are still valid, the external memory data of the
corresponding address is output to the external data bus.
L When writing data
Data is written in both the internal and the external memory.
3800 GROUP USER’S MANUAL
3-21