Fujitsu MB91150 Series, Hardware Manual, Page: 349 / 512

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CHAPTER 15 UART
15.8.3 Baud Rate Based on the External clock
This section shows the settings and equations for calculating the baud rate when the
external clock is selected as the UART transfer clock.
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Baud rate based on the external clock
The following three settings are necessary for selecting the baud rate based on the external
clock.
• Set the SCKE bit of the mode register (SMR0-3) to 0 and set the pins as the external clock-
input pins.
• Set the bits CS2 to CS0 of the mode register (SMR0-3) to 111
B
and select the baud rate
based on the external clock.
The baud rate is selected based on the external clock input from the SCK0 to SCK3 pins as
shown in Figure 15.8-3 "Circuit for baud rate selection based on the external clock". To change
the baud rate, the cycle of the external input clock must be changed because the internal
division ratio is fixed.
Figure 15.8-3 Circuit for baud rate selection based on the external clock
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Equation for baud-rate calculation
Asynchronous baud rate = f/16
Synchronous baud rate = f
f: External clock frequency
(The maximum of f is [frequency of peripheral operation clock]/8. With a frequency of the
peripheral operation clock of 31.9488 MHz, the maximum of f is 3.9936 MHz.)
SCK0-3
Pins
SMR0-3: CS2/1/0=111
(Internal timer selection)
Clock selector
Baud rate
SMR0-3: MD1
(Clock synchronous/asynchronous selection)
1/1 (synchronous)
1/16 (asynchronous)
B