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Is it necessary to set port mode register in using alternate function?

Latest Updated:12/01/2011

Question:

In the uPD78421x, the port I/O status can be set using the port mode register.
Is it necessary to set the port mode register even when using port alternate functions?
(Address bus, data bus, UART, BUZ, etc.)

Answer:

Yes, this is basically correct.
However, regarding the external bus, the function is switched to address bus or data bus by setting the MM register.
So the port mode settings are not required.
When using UART, the mode of the ports corresponding to TxD must be set to output and 0 must be written to the output latch.
The mode of the ports corresponding to RxD must be set to input. Regarding BUZ, PM24 must be set to output and the P24 output latch must be set to 0.
Suitable Products
RL78 Family
78K Family