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12
12.6 Transmit Operation in UART Mode
12.6.1 Setting the UART Baud Rate
The baud rate (data transfer rate) in UART mode is determined by a transmit/receive shift clock. During UART
mode, the source for this transmit/receive shift clock is always the internal clock no matter how the internal/
external clock select bit (SIO Transmit/Receive Mode Register bit 11) is set.
(1) Calculating the UART mode baud rate
After being divided by a clock divider, f(BCLK) is supplied to the Baud Rate Generator (BRG), after which it
is further divided by 16 to produce a transmit/receive shift clock.
The clock divider's divide-by value is selected from 1, 8, 32 or 256 by using the SIO Transmit Control Regis-
ter CDIV (baud rate generator count source select) bits (bits 2–3).(Note 1)
The Baud Rate Generator divides the clock divider output by (baud rate register set value + 1) and further by
16, thus generating a transmit/receive shift clock.
When the internal clock is selected in UART mode, the baud rate is calculated using the equation below.
Baud rate =
[bps]
Baud rate register set value = H'00 to H'FF (Note 1)
Clock divider's divide-by value = 1, 8, 32 or 256
Note 1: If divide-by-1 (i.e., f(BCLK) itself) is selected as the baud rate generator count source,
12.6.2 UART Transmit/Receive Data Formats
The transmit/receive data format during UART mode is determined by setting the SIO Transmit/Receive Mode
Register. Shown below is the transmit/receive data format that can be used in UART mode.
LSB
ST
b7
Start
bit
Figure 12.6.1 Example of a Transfer Data Format during UART Mode
Clock divider's divide-by value x (baud rate register set value + 1) x 16
make sure the value set in the baud rate register is equal to or greater than 7.
Transmit data
Data bits (8 bits)
b6
b5
b4
b3
12.6 Transmit Operation in UART Mode
f(BCLK)
MSB
b2
b1
b0
PAR
Parity
bit
12-40
Serial I/O
Next
data
SP
SP
ST
Stop
bit
32180 Group User's Manual (Rev.1.0)
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