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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.
Table 10.6-1 UART Operation Modes
Mode
0
1
2
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):
•
CLK synchronous:
Peripheral machine clock frequency
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.
Parity
Data length
Yes/No
7
Yes/No
8
No
8 + 1
No
8
/ (16 × )
/
Operation mode
Asynchronous (start-stop) normal
mode
Asynchronous (start-stop)
multiprocessor mode
CLK synchronous mode
10.6 UART Operation
Stop-bit
length
1 bit or 2 bits
No bit
255
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