CHAPTER 2 PIN FUNCTIONS
Preliminary User’s Manual U19014EJ1V0UD
25
2.2.5 P120 to P122 (port 12)
P120 to P122 function as a 3-bit I/O port. These pins also function as pins for external interrupt request input,
connecting resonator for main system clock, and external clock input for main system clock. The following operation
modes can be specified in 1-bit units.
(1) Port
mode
P120 to P122 function as a 3-bit I/O port. P120 to P122 can be set to input or output port using port mode
register 12 (PM12). Only for P120, use of an on-chip pull-up resistor can be specified by pull-up resistor option
register 12 (PU12).
(2) Control
mode
P120 to P122 function as pins for external interrupt request input, connecting resonator for main system clock,
and external clock input for main system clock.
(a) INTP0
This functions as an external interrupt request input (INTP0) for which the valid edge (rising edge, falling
edge, or both rising and falling edges) can be specified.
(b) X1, X2
These are the pins for connecting a resonator for main system clock.
(c) EXCLK
This is an external clock input pin for main system clock.
Caution When writing the flash memory with a flash memory programmer, connect P121/X1/OCD0A as
follows.
•
P121/X1/OCD0A: When using this pin as a port, connect it to V
SS
via a resistor (10 k
Ω
:
recommended) (in the input mode) or leave it open (in the output mode).
The above connection is not necessary when writing the flash memory by means of self
programming.
Remark
Only for the
µ
PD78F0730, X1 and X2 can be used as on-chip debug mode setting pins (OCD0A,
OCD0B) when the on-chip debug function is used. For how to connect an in-circuit emulator supporting
on-chip debugging (QB-78K0MINI), see
CHAPTER 22 ON-CHIP DEBUG FUNCTION.
2.2.6 RESET
This is the active-low system reset input pin.
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