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20.6
UART2, UART3 Baud Rates
One of the following can be selected for the UART2, UART3 serial clock source:
• Dedicated baud rate generator (Reload Counter)
• External clock as it is (clock input to the SCK2/SCK3 pin)
• External clock connected to the baud rate generator (Reload Counter)
■ UART2, UART3 Baud Rate Selection
Table 20.6-1 shows the select circuit of the baud rate. One of the following three types of baud rates can be
selected:
●
Baud rates determined using the dedicated baud rate generator (reload counter)
UART2, UART3 has two independent internal reload counters for transmission and reception serial clock.
The baud rate can be selected via the 15-bit reload value determined by the Baud Rate Generator Register 0
and 1 (BGR02/BGR03 and BGR12/BGR13).
The reload counter divides the machine clock by the value set in the Baud Rate Generator Register 0 and 1.
These baud rates are used in asynchronous mode or synchronous mode (master). To set the clock source,
select the internal clock and the use of the baud rate generator clock (SMR2/SMR3:EXT=0, OTO=0).
●
Baud rates determined using external clock (one-to-one mode)
The clock input from UART2, UART3 clock pulse input pins (SCK2/SCK3) is used as it is (synchronous).
Any baud rate less than the machine clock divided by 4 and is divisible can be set externally. These baud
rates are used in synchronous mode (slave). To set the clock source, select the external clock and its direct
use (SMR2/SMR3:EXT=1, OTO=1).
●
Baud rates determined using the dedicated baud rate generator with external clock
An external clock source can also be connected internally to the reload counter. In this mode it is used
instead of the internal machine clock. Baud rates can be selected by setting baud rate generator registers 1
and 0 (BGR02/BGR03, BGR12/BGR13) to 15-bit reload values. The reload counter divides the external
clock frequency by the set value. These baud rates are used in asynchronous mode. To set the clock source,
select the external clock and the use of the baud rate generator clock (SMR2/SMR3:EXT=1, OTO=0). This
was designed to use quartz oscillators with special frequencies and having the possibility to divide them.
CHAPTER 20 UART2, UART3
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