R8C/20 Group, R8C/21 Group 15. Serial Interface
Rev.2.00 Aug 27, 2008 Page 277 of 458
REJ09B0250-0200
i = 0 or 1
NOTES:
1. The bits used for transmit/receive data are as follows: Bits 0 to 6 when transfer data is 7-bit long; bits
0 to 7 when transfer data is 8-bit long; bits 0 to 8 when transfer data is 9-bit long.
2. The following bits are undefined: Bits 7 and 8 when transfer data is 7 bits long; bit 8 when transfer
data is 8 bits long.
3. External clock can be selected in UART0 only.
Table 15.6 lists the I/O Pin Functions in UART Mode. After the UARTi (i = 0 or 1) operating mode is selected, the
TXDi pin outputs “H” level (if the NCH bit is set to 1 (N-channel open-drain outputs), this pin is in a high-
impedance state) until transfer starts.
Table 15.5 Registers Used and Settings for UART Mode
Register Bit Function
UiTB 0 to 8
Set transmit data
(1)
UiRB 0 to 8
Receive data can be read
(1, 2)
OER,FER,PER,SUM Error flag
UiBRG 0 to 7 Set a bit rate
UiMR SMD2 to SMD0 Set to 100b when transfer data is 7-bit long
Set to 101b when transfer data is 8-bit long
Set to 110b when transfer data is 9-bit long
CKDIR
Select the internal clock or external clock
(3)
STPS Select the stop bit
PRY, PRYE Select whether parity is included and odd or even
UiC0 CLK0, CLK1 Select the count source for the UiBRG register
TXEPT Transmit register empty flag
NCH Select TXDi pin output mode
CKPOL Set to 0
UFORM LSB first or MSB first can be selected when transfer data is 8-bit
long. Set to 0 when transfer data is 7- or 9-bit long.
UiC1 TE Set to 1 to enable transmit
TI Transmit buffer empty flag
RE Set to 1 to enable receive
RI Receive complete flag
UiIRS Select the UARTi transmit interrupt source
UiRRM Set to 0
Table 15.6 I/O Pin Functions in UART Mode
Pin name Function Selection Method
TXD0(P1_4) Output serial data (Cannot be used as a port when performing receive only)
RXD0(P1_5) Input serial data The PD1_5 bit in the PD1 register = 0
(P1_5 can be used as an input port when performing transmit only)
CLK0(P1_6) Programmable I/O port The CKDIR bit in the U0MR register = 0
Input transfer clock The CKDIR bit in the U0MR register = 1
The PD1_6 bit in the PD1 register = 0
TXD1(P6_6) Output serial data U1PINSEL bit in PMR register = 1
(Cannot be used as a port when performing receive only)
RXD1(P6_7) Input serial data U1PINSEL bit in PMR register = 1
The PD6_7bit in the PD6 register = 0
(P6_7 can be used as an input port when performing transmit
only)
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