Fujitsu MB90460 Series, Hardware Manual, Page: 516 / 739

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CHAPTER 17 UART
17.6.3 Baud Rates Determined Using the External Clock
This section describes the settings used when the external clock is selected as the
UART transfer clock. It also shows the baud rate calculation formulas.
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Baud Rates determined using the External Clock
The following three settings are required to select the baud rate determined by using the external clock:
• Write 111
B
to the CS2 to CS0 bits of the mode control register (SMR0/SMR1) to select the baud rate
determined by using the external clock input.
• Set the P42/SCK0 and P62/SCK1 pins as input ports (DDR4: bit2 = 0 and DDR6: bit2 = 0).
• Write "0" to the SCKE bit of the mode control register (SMR0/SMR1) to set the pin as an external clock
input pin.
As shown in Figure 17.6-3, a baud rate is selected using the external clock input from the SCK1 pin. To
change the baud rate, the external input clock cycle must be changed because the internal division ratio is
fixed.
Figure 17.6-3 Baud Rate Selection Circuit for the External Clock
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Baud rate calculation formulas
Asynchronous baud rate = f/16
Synchronous baud rate = f
f: External clock frequency (up to 2 MHz)
1/1 (synchronous)
1/16 (asynchronous)
SMR0/SMR1 : CS2 to CS0 = 111
B
(Selects the external clock)
Baud rate
SMR0/SMR1 : MD1
(Synchronous or asynchronous clock selection)
Clock selector
P42/SCK0
P62/SCK1
Pin
SCKI