NEC 78K0R/KE3 User Manual page 120

4.2.9 Port 12
P120 is a 1-bit I/O port with an output latch. Port 12 can be set to the input mode or output mode in 1-bit units
using port mode register 12 (PM12). When used as an input port, use of an on-chip pull-up resistor can be specified
by pull-up resistor option register 12 (PU12).
P121 to P124 are 4-bit input ports.
This port can also be used for external interrupt request input, potential input for external low-voltage detection,
connecting resonator for main system clock, connecting resonator for subsystem clock, and external clock input for
main system clock.
Reset signal generation sets port 12 to input mode.
Figures 4-23 to 4-25 show block diagrams of port 12.
Caution The function setting on P121 to P124 is available only once after the reset release. The port once
set for connection to an oscillator cannot be used as an input port unless the reset is performed.
WR
PU
RD
WR
PORT
Output latch
WR
PM
P12: Port register 12
PU12: Pull-up resistor option register 12
PM12: Port mode register 12
RD: Read signal
WR××: Write signal
120
CHAPTER 4 PORT FUNCTIONS
Figure 4-23. Block Diagram of P120
PU12
PU120
Alternate
function
P12
(P120)
PM12
PM120
User's Manual U17854EJ9V0UD
EV
DD
P-ch
P120/INTP0/EXLVI