UPD784938 Datasheet, PDF (460/733 Pages) NEC – 16-Bit Single-Chip Microcontrollers

CHAPTER 19 3-WIRE SERIAL I/O MODE
Notes 1. When the external clock is selected, the usable serial clock is MIN fXX/8 in the case of fCLK = fXX/1; otherwise,
it is MIN fCLK/4.
2. Setting is prohibited when the system clock (fCLK = fXX/8) is selected.
Caution When bit 3 is set, the P-ch of the output buffer is forcibly turned OFF. This channel is not affected
by PM3 and PMC3, or PM10 and PMC10. Therefore, if the input or output mode is changed by using
the PM register with bit 3 set in the port mode, the content of the port latch can be output and the pin
level can be read in the N-ch open-drain mode.
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Preliminary User’s Manual U13987EJ1V0UM00