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CHAPTER 15 UART
15.8.1 Baud Rate Based on the Dedicated Baud-Rate Generator
This section shows the baud rates that can be set when the output clock of the
dedicated baud-rate generator is selected as the UART transfer clock.
I Baud rate based on the dedicated baud-rate generator
When the dedicated baud-rate generator is used to generate the transfer clock, the machine
clock prescaler is used to divide the machine clock rate by the transfer clock division ratio
selected with the clock selector. The machine clock division ratio is common in asynchronous
and synchronous modes, but the transfer clock division ratio differs in asynchronous and
synchronous modes. The values internally set separately for asynchronous and synchronous
modes are selected.
Therefore, the actual baud rate can be expressed in the following equations.
Asynchronous baud rate = φ (prescaler division ratio) x (asynchronous transfer clock division
•
ratio)
Synchronous baud rate = φ (prescaler division ratio) x (synchronous transfer clock division
•
ratio)
φ: Machine clock frequency
❍ Division ratio based on the prescaler (common for asynchronous and synchronous
modes)
The machine clock division ratio is determined in accordance with the DIV3 to DIV0 bits of the
CDCR register as shown in Table 15.8-1 "Selection of division ratio based on the machine clock
prescaler".
Table 15.8-1 Selection of division ratio based on the machine clock prescaler
MD
0
1
1
1
1
1
1
1
1
1
1
1
328
DIV3
DIV2
-
-
0
0
0
0
0
0
0
0
0
1
0
1
0
1
0
1
1
0
1
0
1
0
DIV1
DIV0
-
-
0
0
0
1
1
0
1
1
0
0
0
1
1
0
1
1
0
0
0
1
1
0
div
Stop
1
2
3
4
5
6
7
8
9
10
11
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