RL78/G1P
CHAPTER 4 PORT FUNCTIONS
R01UH0895EJ0100 Rev.1.00
81
Nov 29, 2019
4.2.6 Port 12
P121 and P122 are 2-bit input only ports.
This port can also be used for connecting resonator for main system clock and external clock input for main system
clock.
Reset signal generation sets port 12 to input mode.
Table 4-9. Settings of Registers When Using Port 12
Name
I/O
Alternate Function Setting
Remark
P121
Input
OSCSEL bit of CMC register = 0
or EXCLK bit = 1
P122
Input
OSCSEL bit of CMC register = 0
Caution The function setting on P121 and P122 is available only once after the reset release. The port once
set for connection to an X1 oscillator, external clock input cannot be used as an input port unless the
reset is performed.
Figure 4-14 shows a block diagram of port 12.
Figure 4-14. Block Diagram of P121 and P122
P122/X2/EXCLK
RD
EXCLK, OSCSEL
CMC
OSCSEL
CMC
Clock generator
P121/X1
RD
Internal bus
CMC: Clock operation mode control register
RD: Read
signal
Summary of Contents for RL78/G1P
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