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10.6 UART Operation
10.6 UART Operation
UART has the following three operation modes, which can be changed by setting a
value in the SMR or SCR register.
• Asynchronous (start-stop) normal mode
• Asynchronous (start-stop) multiprocessor mode
• CLK synchronous mode
■
UART Operation Modes
Table 10.6-1 summarizes the UART operation modes.
Stop-bit length in asynchronous (start-stop) mode can be specified only for transmission. Stop-
bit length for data reception is always 1 bit. The UART does not operate in a mode other than
those listed below.
■
UART Clock Selection
❍
Internal timer
When the U-TIMER is selected while CS0 is set to "0", the baud rate is determined by the
reload value set for the U-TIMER. The baud rate is calculated as follows:
• Asynchronous (start-stop):
φ
/ (16
×
β
)
• CLK synchronous:
φ
/
β
φ:
Peripheral machine clock frequency
β:
Cycle set by the U-TIMER (2n+2 or 2n+3, where n is a reload value)
The baud rate for transmission in asynchronous (start-stop) mode can range from -1% to +1%
of the determined baud rate.
Table 10.6-1 UART Operation Modes
Mode Parity Data length Operation mode Stop-bit
length
0 Yes/No 7 Asynchronous (start-stop) normal
mode
1 bit or 2 bits
Yes/No 8
1 No 8 + 1 Asynchronous (start-stop)
multiprocessor mode
2 No 8 CLK synchronous mode No bit