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CHAPTER 13 UART
MB90560 series
13.6
UART Baud Rates
13.6.1 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.
I
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 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
x (prescaler division ratio) x (asynchronous transfer clock
division ratio)
synchronous baud rate =
φ
x (prescaler division ratio) x (synchronous transfer clock division
ratio)
φ
: Machine clock frequency
G
Division Ratios for the Prescaler (Common to Asynchronous and Synchronous Baud
Rates)
Each machine clock division ratio is selected using the DIV3 to DIV0 bits of the CDCR register
as listed in Table 13.6-1.
Table 13.6-1 Selection of each division ratio for the machine clock prescaler
MD
DIV3
DIV2
DIV1
DIV0
Divided by
(div)
0
–
–
–
–
stop
1
0
0
0
0
1
1
0
0
0
1
2
1
0
0
1
0
3
1
0
0
1
1
4
1
0
1
0
0
5
1
0
1
0
1
6
1
0
1
1
0
7
1
0
1
1
1
8