
R8C/38T-A Group
19. Serial Interface (UART0)
Under development Preliminary document
Specifications in this document are tentative and subject to change.
R01UH0241EJ0010 Rev.0.10
Page 388 of 730
Aug 05, 2011
19.3.1.1
Operation Examples
Figure 19.3
Transmit and Receive Timing in Clock Synchronous Serial I/O Mode
Transfer clock
Transmit timing example (internal clock selected)
Data is set in U0TB register
TE bit in
U0C1 register
TI bit in
U0C1 register
CLK
TXD
TXEPT bit in
U0C0 register
From U0TB register to UART0 transmit register
Stops because TE bit is 0
TC
fEXT: Frequency of external clock
The above diagram applies for the following settings:
CKDIR bit in U0MR register = 1 (external clock)
CKPOL bit in U0C0 register = 0 (transmit data is output at the falling
edge and receive data is input at the rising edge of the transfer clock)
The following requirements must be met when an input
to the CLK0 pin is high before data reception:
TE bit in U0C1 register
1 (transmission enabled)
RE bit in U0C1 register
1 (reception enabled)
Dummy data is written to U0TB register
RE bit in
U0C1 register
Receive timing example (external clock selected)
Dummy data is set in U0TB register
TE bit in
U0C1 register
TI bit in
U0C1 register
CLK
RXD
RI bit in
U0C1 register
From U0TB register to UART0 transmit register
Receive data is acquired
From UART0 receive
register to U0RB register
U0RB register is read
1/fEXT
TCLK
D0 D1 D2 D3 D4 D5 D6 D7 D0 D1 D2 D3 D4 D5 D6
D7
D0 D1 D2 D3 D4 D5 D6
D7
D0 D1 D2 D3 D4 D5 D6
D7
D0 D1 D2 D3 D4 D5 D6
The above diagram applies for the following settings:
CKDIR bit in U0MR register = 0 (internal clock)
CKPOL bit in U0C0 register = 0 (transmit data is output at the falling
edge and receive data is input at the rising edge of the transfer clock)
U0IRS bit in U0C1 register = 0 (transmit buffer empty)
TC = TCLK = 2 (n + 1)/fi
fi: Frequency of U0BRG count source (f1, f8, f32, or fC1)
n: Value set in U0BRG register
1/fi
1/f1