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CHAPTER 17 UART
17.6.1
Baud Rates Determined Using the Dedicated Baud Rate
Generator
This section describes the baud rates that can be set when the clock from the dedicated
baud rate generator is selected as the UART transfer clock.
■ Baud Rates determined using the Dedicated Baud Rate Generator
When the transfer clock is generated using the dedicated baud rate generator, the machine clock is divided
with the machine clock prescaler. The divided machine clock is then divided by the transfer clock division
ratio selected with the clock selector again.The machine clock division ratios are common to the
asynchronous and synchronous baud rates, but different values set internally are selected as the transfer
clock division ratio for the asynchronous and synchronous baud rates.
The actual transfer rate can be calculated using the following formulas:
asynchronous baud rate = φ × (prescaler division ratio) × (asynchronous transfer clock division ratio)
synchronous baud rate = φ × (prescaler division ratio) × (synchronous transfer clock division ratio)
φ : Machine clock frequency
●
Division ratios for the prescaler (common to asynchronous and synchronous baud rates)
Each machine clock division ratio is selected using the DIV2 to DIV0 bits of the CDCR register as listed in
Table 17.6-1
Table 17.6-1 Selection of Each Division Ratio for the Machine Clock Prescaler
MD
0
1
1
1
1
1
1
1
1
492
DIV2
DIV1
–
–
0
0
0
0
0
1
0
1
1
0
1
0
1
1
1
1
DIV0
–
Setting not allowed
0
1
0
1
0
1
0
1
div
1
2
3
4
5
6
7
8
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