R8C/20 Group, R8C/21 Group 15. Serial Interface
Rev.2.00 Aug 27, 2008 Page 273 of 458
REJ09B0250-0200
Figure 15.7 Transmit and Receive Timing Example in Clock Synchronous Serial I/O Mode
Transfer clock
D0
TE bit in U0C1
register
TXD0
• Example of transmit timing (when internal clock is selected)
Set data in U0TB register
Transfer from U0TB register to UART0 transmit register
TC
CLK0
TCLK
Stop pulsing because the TE bit is set to 0
D1 D2 D3 D4 D5 D6 D7 D0 D1 D2 D3 D4 D5 D6 D7 D0 D1 D2 D3 D4 D5 D6 D7
TC = TCLK = 2(n+1)/fi
fi: Frequency of UiBRG count source (f1, f8, f32)
n: Setting value to UiBRG register
The above applies under the following settings:
• CKDIR bit in U0MR register = 0 (internal clock)
• CKPOL bit in U0C0 register = 0 (output transmit data at the falling edge and input receive data at the rising edge of the transfer clock)
• U0IRS bit in U0C1 register = 0 (an interrupt request is generated when the transmit buffer is empty)
D0
Set to 0 when interrupt request is acknowledged, or set by a program
Write dummy data to U0TB register
Transfer from U0TB register to UART0 transmit register
1/fEXT
D1 D2 D3 D4 D5 D6 D7 D0 D1 D2 D3 D4 D5
Receive data is taken in
Read out from U0RB register
Transfer from UART0 receive register to
U0RB register
TI bit in U0C1
register
1
0
1
0
1
0
1
0
TXEPT bit in
U0C0 register
IR bit in S0TIC
register
Set to 0 when interrupt request is acknowledged, or set by a program
• Example of receive timing (when external clock is selected)
RE bit in U0C1
register
TE bit in U0C1
register
TI bit in U0C1
register
1
0
1
0
1
0
RI bit in U0C1
register
IR bit in S0RIC
register
1
0
1
0
CLK0
RXD0
The above applies under the following settings:
• CKDIR bit in U0MR register = 1 (external clock)
• CKPOL bit in U0C0 register = 0 (output transmit data at the falling edge and input receive data at the rising edge of the transfer clock)
The following conditions are met when “H” is applied to the CLK0 pin before receiving data:
• TE bit in U0C1 register = 1 (enables transmit)
• RE bit in U0C1 register = 1 (enables receive)
• Write dummy data to the U0TB register
fEXT: Frequency of external clock
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