Renesas M32R/ECU Series User Manual page 809

Appendix 4
Appendix 4.5 Precautions To Be Observed after Reset
Appendix 4.5.1 Input/output Ports
After reset, the microcomputer's input/output ports are disabled against input in order to prevent current from
flowing through the port. To use any ports in input mode, set the Port Input Special Function Control Register
(PICNT) PIEN0 bit to enable them for input. For details, see Section 8.3, "Input/Output Port Related Registers."
Appendix 4.6 Precautions about Input/Output Ports
Appendix 4.6.1 When Using Input/Output Ports in Output Mode
Because the value of the Port Data Register is undefined after reset, the Port Data Register must have its initial
value set in it before the Port Direction Register can be set for output. Conversely, if the Port Direction Register
is set for output before setting data in the Port Data Register, the Port Data Register outputs an undefined value
until any data is written into it.
Appendix 4.6.2 About the Port Input Disable Function
Because the input/output ports are disabled against input after reset, they must be enabled for input by setting
the Port Input Enable (PIEN0) bit to "1" before their input functions can be used.
When disabled against input, the input/output ports are in a state equivalent to a situation where the pin has a
low-level input applied. Consequently, if a peripheral input function is selected for any port (uncontrolled pin)
while disabled against input by using the Port Operation Mode Register, the port may operate unexpectedly due
to the low-level input on it.
Appendix 4.5 Precautions To Be Observed after Reset
Appendix 4-4
SUMMARY OF PRECAUTIONS
32180 Group User's Manual (Rev. 1.0)