7643_06 Datasheet, PDF (358/424 Pages) Renesas Technology Corp – 8-BIT SINGLE-CHIP MICROCOMPUTER

7643 Group
APPENDIX
3.3 Notes on use
(3) Pull-up control
When using port P2, which includes a pull-up resistor, as an output port, its port pull-up control
is invalidated, that is, pull-up cannot be enabled.
q Reason
Pull-up/pull-down control is valid only when each direction register is set to the input mode.
3.3.12 Notes on programming
(1) Processor status register
➀ Initializing of processor status register
Flags which affect program execution must be initialized after a reset.
In particular, it is essential to initialize the T and D flags because they have an important effect
on calculations.
q Reason
After a reset, the contents of the processor status register (PS) are undefined except for the
I flag which is “1”.
Reset
↓
Initializing of flags
↓
Main program
Fig. 3.3.5 Initialization of processor status register
Rev.2.00 Aug 28, 2006 page 35 of 98
REJ09B0133-0200