R8C/1A Group, R8C/1B Group
5. Programmable I/O Ports
Rev.1.30
Dec 08, 2006
Page 37 of 315
REJ09B0252-0130
5.5
Unassigned Pin Handling
Table 5.18 lists Unassigned Pin Handling. Figure 5.11 shows Unassigned Pin Handling.
NOTES:
1. If these ports are set to output mode and left open, they remain in input mode until they are switched
to output mode by a program. The voltage level of these pins may be undefined and the power
supply current may increase while the ports remain in input mode.
The content of the direction registers may change due to noise or program runaway caused by
noise. In order to enhance program reliability, the program should periodically repeat the setting of
the direction registers.
2. Connect these unassigned pins to the MCU using the shortest wire length (2 cm or less) possible.
3. When the power-on reset function is in use.
Figure 5.11
Unassigned Pin Handling
Table 5.18
Unassigned Pin Handling
Pin Name
Connection
Ports P1, P3_3 to P3_5,
P3_7, P4_5
• After setting to input mode, connect each pin to VSS via a resistor (pull-
down) or connect each pin to VCC via a resistor (pull-up).
(2)
• After setting to output mode, leave these pins open.
(1, 2)
Ports P4_6, P4_7
Connect to VCC via a pull-up resistor
(2)
Port P4_2/VREF
Connect to VCC
RESET
(3)
Connect to VCC via a pull-up resistor
(2)
NOTE:
1. When the power-on reset function is in use.
MCU
Port P1, P3_3 to P3_5,
P3_7, P4_5
(Input mode)
:
:
(Input mode)
(Output mode)
Port P4_6, P4_7
RESET
(1)
Port P4_2/VREF
:
:
Open