Atmel C51 Manual Página 97

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Common Features Description
2-97 Atmel 8051 Microcontrollers Hardware Manual
4316E–8051–01/07
2.13.1 Baud Rates The baud rate in Mode 0 is fixed:
The baud rate in Mode 2 depends on the value of bit SMOD in Special Function Regis-
ter PCON.
If SMOD = 0 (which is its value on reset), the baud rate is 1/64 the oscillator frequency.
If SMOD = 1, the baud rate is 1/32 the oscillator frequency.
In the 80C51, the baud rates in Modes 1 and 3 are determined by the Timer 1 overflow
rate. In case of Timer2, these baud rates can be determined by Timer 1, or by Timer 2,
or by both (one for transmit and the other for receive).
Baud Rate Selection for
UART for Mode 1 and 3
The Baud Rate Generator for transmit and receive clocks can be selected separately via
the T2CON and BDRCON registers.
Figure 2-19. Baud Rate Selection
2.13.2 Baud Rate Selection
Table for UART
RCLK
/ 16
RBCK
INT_BRG
0
1
TIMER1
0
1
0
1
TIMER2
INT_BRG
TIMER1
TIMER2
TIMER_BRG_RX
Rx Clock
/ 16
0
1
TIMER_BRG_TX
Tx Clock
TBCK
TCLK
TCLK
(T2CON)
RCLK
(T2CON)
TBCK
(BDRCON)
RBCK
(BDRCON)
Clock Source
UART Tx
Clock Source
UART Rx
0 0 0 0 Timer 1 Timer 1
1 0 0 0 Timer 2 Timer 1
0 1 0 0 Timer 1 Timer 2
1 1 0 0 Timer 2 Timer 2
X 0 1 0 INT_BRG Timer 1
X 1 1 0 INT_BRG Timer 2
0 X 0 1 Timer 1 INT_BRG
1 X 0 1 Timer 2 INT_BRG
X X 1 1 INT_BRG INT_BRG
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