Renesas RL78/G1P Hardware User Manual page 100

RL78/G1P
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.
Name
P121
P122
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.
RD
RD
CMC: Clock operation mode control register
RD: Read signal
R01UH0895EJ0100 Rev.1.00
Nov 29, 2019
Table 4-9. Settings of Registers When Using Port 12
I/O
Input OSCSEL bit of CMC register = 0
Input OSCSEL bit of CMC register = 0
Figure 4-14. Block Diagram of P121 and P122
Clock generator
Alternate Function Setting
or EXCLK bit = 1
CMC
OSCSEL
CMC
EXCLK, OSCSEL
CHAPTER 4 PORT FUNCTIONS
Remark
P122/X2/EXCLK
P121/X1
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