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13 UART (UART3)
13.2 Input/Output Pins and External Connections
13.2.1 List of Input/Output Pins
Table 13.2.1.1 lists the UART3 pins.
Pin name
USINn
USOUTn
If the port is shared with the UART3 pin and other functions, the UART3 input/output function must be assigned to
the port before activating the UART3. For more information, refer to the "I/O Ports" chapter.
13.2.2 External Connections
Figure 13.2.2.1 shows a connection diagram between the UART3 in this IC and an external UART device.
Figure 13.2.2.1 Connections between UART3 and an External UART Device
13.2.3 Input Pin Pull-Up Function
The UART3 includes a pull-up resistor for the USINn pin. Setting the UART3_nMOD.PUEN bit to 1 enables the
resistor to pull up the USINn pin.
13.2.4 Output Pin Open-Drain Output Function
The USOUTn pin supports the open-drain output function. Default configuration is a push-pull output and it is
switched to an open-drain output by setting the UART3_nMOD.OUTMD bit to 1.
13.2.5 Input/Output Signal Inverting Function
The UART3 can invert the signal polarities of the USINn pin input and the USOUTn pin output by setting the
UART3_nMOD.INVRX bit and the UART3_nMOD.INVTX bit, respectively, to 1.
Note: Unless otherwise specified, this chapter shows input/output signals with non-inverted wave-
forms (UART3_nMOD.INVRX bit = 0, UART3_nMOD.INVTX bit =0).
13.3 Clock Settings
13.3.1 UART3 Operating Clock
When using the UART3 Ch.n, the UART3 Ch.n operating clock CLK_UART3_n must be supplied to the UART3
Ch.n from the clock generator. The CLK_UART3_n supply should be controlled as in the procedure shown below.
1. Enable the clock source in the clock generator if it is stopped (refer to "Clock Generator" in the "Power Supply,
Reset, and Clocks" chapter).
2. Set the following UART3_nCLK register bits:
- UART3_nCLK.CLKSRC[1:0] bits
- UART3_nCLK.CLKDIV[1:0] bits
The UART3 operating clock should be selected so that the baud rate generator will be configured easily.
13-2
Table 13.2.1.1 List of UART3 Pins
I/O*
Initial status*
I
I (Hi-Z)
O
O (High)
* Indicates the status when the pin is configured for the UART3.
USINn
USOUTn
S1C31 UART3
(Clock source selection)
(Clock division ratio selection = Clock frequency setting)
Seiko Epson Corporation
Function
UART3 Ch.n data input pin
UART3 Ch.n data output pin
OUT
IN
External UART
S1C31D41 TECHNICAL MANUAL
(Rev. 1.1)
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