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CHAPTER 13 UART
MB90560 series
13.6
13.6.2 Baud Rates Determined Using the Internal Timer (16-bit
Reload Timer 0)
UART Baud Rates
This section describes the settings used when the internal clock supplied from 16-bit
reload timer 0 is selected as the UART transfer clock. It also shows the baud rate
calculation formulas.
I
Baud Rates Determined Using the Internal Timer (16-bit Reload Timer 0)
Writing 110
B
to the CS2 to CS0 bits of the mode control register (SMR0/1) selects the baud rate
determined using the internal timer. Any baud rate can be set by specifying a prescaler division
ratio and reload value for 16-bit reload timer 0. Figure 13.6-2 shows the baud rate selection
circuit for the internal timer.
Figure 13.6-2 Baud rate selection circuit for the internal timer (16-bit reload timer 0)
G
Baud Rate Calculation Formulas
φ
: Machine clock frequency
X: Division ratio for the prescaler of 16-bit reload timer 0 (2
1
, 2
3
, or 2
5
)
n: Reload value for 16-bit reload timer 0 (0 to 65535)
SMR1 : CS2~0="110
B
"
(Selects the internal timer.)
SMR1 MD1, MD0
(Clock synchronous/asynchronous selection)
Clock selector
16-bit reload timer output
(the frequency is specified with a prescaler
division ratio and reload value.)
1/1 (synchronous)
1/16 (asynchronous)
Baud rate
Asynchronous baud rate =
φ
X (n + 1) x 2 x 16
bps
Synchronous baud rate =
φ
bps
X (n + 1) x 2