12 UART (UART3)
12-2
Seiko Epson Corporation
S1C17M20/M21/M22/M23/M24/M25
TECHNICAL MANUAL (Rev. 1.0)
12.2 Input/Output Pins and External Connections
12.2.1 List of Input/Output Pins
Table 12.2.1.1 lists the UART3 pins.
Table 12.2.1.1 List of UART3 Pins
Pin name
I/O
*
Initial status
*
Function
USINn
I
I (Hi-Z)
UART3 Ch.n data input pin
USOUTn
O
O (High)
UART3 Ch.n data output pin
*
Indicates the status when the pin is configured for the UART3.
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.
12.2.2 External Connections
Figure 12.2.2.1 shows a connection diagram between the UART3 in this IC and an external UART device.
USINn
USOUTn
OUT
IN
S1C17 UART3
External UART
Figure 12.2.2.1 Connections between UART3 and an External UART Device
12.2.3 Input Pin Pull-Up Function
The UART3 includes a pull-up resistor for the USIN
n
pin. Setting the UA
n
MOD.PUEN bit to 1 enables the resistor
to pull up the USIN
n
pin.
12.2.4 Output Pin Open-Drain Output Function
The USOUT
n
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 UA
n
MOD.OUTMD bit to 1.
12.2.5 Input/Output Signal Inverting Function
The UART3 can invert the signal polarities of the USIN
n
pin input and the USOUT
n
pin output by setting the UA
n-
MOD.INVRX bit and the UA
n
MOD.INVTX bit, respectively, to 1.
Note: Unless otherwise specified, this chapter shows input/output signals with non-inverted wave-
forms (UAnMOD.INVRX bit = 0, UAnMOD.INVTX bit =0).
12.3 Clock Settings
12.3.1 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 UA
n
CLK register bits:
- UA
n
CLK.CLKSRC[1:0] bits (Clock source selection)
- UA
n
CLK.CLKDIV[1:0] bits (Clock division ratio selection = Clock frequency setting)
The UART3 operating clock should be selected so that the baud rate generator will be configured easily.