UPD70F3218 Datasheet, PDF (87/884 Pages) NEC – 32-Bit Single-Chip Microcontrollers

CHAPTER 3 CPU FUNCTIONS
The operation conditions of the PRERR flag are described below.
(a) Set conditions (PRERR = 1)
(i) When a write operation to the special register takes place without write operation being performed to
the PRCMD register (when step <3> is performed without performing step <2> as described in 3.4.7
(1) Setting data to special registers).
(ii) When a write operation (including bit manipulation instruction) to an on-chip peripheral I/O register
other than a special register is performed following write to the PRCMD register (when <3> in 3.4.7
(1) Setting data to special registers is not a special register).
Remark
Regarding the special registers other than the WDTM register (PCC and PSC registers), even if
on-chip peripheral I/O register read (except bit manipulation instruction) (internal RAM access,
etc.) is performed in between write to the PRCMD register and write to a special register, the
PRERR flag is not set and setting data can be written to the special register.
(b) Clear conditions (PRERR = 0)
(i) When 0 is written to the PRERR flag
(ii) When system reset is performed
Cautions 1. If 0 is written to the PRERR bit of the SYS register that is not a special register
immediately following write to the PRCMD register, the PRERR bit becomes 0 (write
priority).
2. If data is written to the PRCMD register that is not a special register immediately
following write to the PRCMD register, the PRERR bit becomes 1.
User’s Manual U16889EJ1V0UD
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