
48
AT89C51RB2/RC2
4180E–8051–10/06
Table 32. Baud Rate Selection Table UART
Internal Baud Rate Generator
(BRG)
When the internal Baud Rate Generator is used, the Baud Rates are determined by the
BRG overflow depending on the BRL reload value, the value of SPD bit (Speed Mode)
in BDRCON register and the value of the SMOD1 bit in PCON register.
Figure 21. Internal Baud Rate
The baud rate for UART is token by formula:
TCLK
(T2CON)
RCLK
(T2CON)
TBCK
(BDRCON)
RBCK
(BDRCON)
Clock Source
UART Tx
Clock Source
UART Rx
0000
Timer 1
1000
Timer 2
Timer 1
0100
Timer 1
Timer 2
1100
Timer 2
X
010
INT_BRG
Timer 1
X
110
INT_BRG
Timer 2
0
X
0
1
Timer 1
INT_BRG
1
X
0
1
Timer 2
INT_BRG
X
1
INT_BRG
0
1
Overflow
SPD
BDRCON.1
BRG
(8 bits)
BRL
(8 bits)
FClk Periph
÷ 6
BRR
BDRCON.4
0
1
SMOD1
PCON.7
÷ 2
INT_BRG
Baud_Rate =
6(1-SPD)
32 (256 -BRL)
2
SMOD1
F
PER
BRL = 256 -
6
(1-SPD)
32 Baud_Rate
2SMOD1
F
PER