Datasheet
173
4341H–MP3–10/07
AT8xC51SND2C/MP3B
20.4.4 Baud Rate Selection (Modes 1 and 3)
In modes 1 and 3, the Baud Rate is derived either from the Timer 1 or the Internal Baud Rate
Generator and allows different baud rate in reception and transmission.
As shown in Figure 20-12 the selection is done using RBCK and TBCK bits in BDRCON register.
Figure 20-13 gives the baud rate calculation formulas for each baud rate source while Table 20-
2 details Internal Baud Rate Generator configuration for different peripheral clock frequencies
and giving baud rates closer to the standard baud rates.
Figure 20-12. Baud Rate Source Selection (Modes 1 and 3)
Figure 20-13. Baud Rate Formulas (Modes 1 and 3)
0
1
RBCK
BDRCON.2
T1
CLOCK
To Serial
IBRG
CLOCK
Rx Port
0
1
TBCK
BDRCON.3
T1
CLOCK
To Serial
IBRG
CLOCK
Tx Port
÷
16
÷
16
Baud_Rate=
6
(1-SPD)
⋅
32
⋅
(256 -BRL)
2
SMOD1
⋅
F
PER
BRL= 256 -
6
(1-SPD)
⋅
32
⋅
Baud_Rate
2
SMOD1
⋅
F
PER
Baud_Rate=
6
⋅
32
⋅
(256 -TH1)
2
SMOD1
⋅
F
PER
TH1= 256 -
192
⋅
Baud_Rate
2
SMOD1
⋅
F
PER
a. IBRG Formula b. T1 Formula