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CHAPTER 13 UART
13.3 Pins of UART
Pins relating to UART are the clock I/O pin (P30/UCK/SCK), serial data output pin
(P31/UO/SO), and serial data input pin (P32/UI/SI).
■ UART Relating Pins
● P30/UCK/SCK
This pin functions as the general-purpose I/O port (P30), UART clock I/O pin (UCK), or 8-bit serial clock
I/O pin (SCK). When clock output is enabled (SMC: SCKE = 1), this pin functions as the UART clock
output pin (UCK) regardless of the value in the corresponding port direction register. When this pin
functions as the UART clock, do not use any external clock (SRC: CS1 and CS0 must be other than 00
B
).
When using this pin as the UART clock input pin, disable clock output (SMC: SCKE = 0) and set it as the
input port using the corresponding port direction register (DDR3: bit0 = 0). In this case, be sure to select
the external clock (SRC: CS1 and CS0 = 00
B
).
● P31/UO/SO
This port functions as the general-purpose I/O port (P31), UART serial data output pin (UO), or 8-bit serial
data output pin (SO). When serial data output is enabled (SMC: SOE = 1), this pin functions as the UART
serial data output pin (UO) regardless of the value in the corresponding port direction register.
● P32/UI/SI
This port functions as the general-purpose I/O port (P32), UART serial data input pin (UI), or 8-bit serial
data input pin (SI). When using this pin as the UART serial data input pin, set this pin as the input port by
using the corresponding port direction register (DDR3: bit2 = 0).