Datasheet
171
4341H–MP3–10/07
AT8xC51SND2C/MP3B
20.3.3 Baud Rate Selection (Mode 0)
In mode 0, the baud rate can be either, fixed or variable.
As shown in Figure 20-6, the selection is done using M0SRC bit in BDRCON register.
Figure 20-7 gives the baud rate calculation formulas for each baud rate source.
Figure 20-6. Baud Rate Source Selection (mode 0)
Figure 20-7. Baud Rate Formulas (Mode 0)
20.4 Asynchronous Modes (Modes 1, 2 and 3)
The Serial Port has one 8-bit and 2 9-bit asynchronous modes of operation. Figure 20-8 shows
the Serial Port block diagram in such asynchronous modes.
Figure 20-8. Serial I/O Port Block Diagram (Modes 1, 2 and 3)
20.4.0.1 Mode 1
Mode 1 is a full-duplex, asynchronous mode. The data frame (see Figure 20-9) consists of 10
bits: one start, eight data bits and one stop bit. Serial data is transmitted on the TXD pin and
received on the RXD pin. When a data is received, the stop bit is read in the RB8 bit in SCON
register.
0
1
M0SRC
BDRCON.0
PER
CLOCK
÷
6
To Serial Port
IBRG0
CLOCK
Baud_Rate=
6
(1-SPD)
⋅
16
⋅
(256 -BRL)
F
PER
BRL= 256
-
6
(1-SPD)
⋅
16
⋅
Baud_Rate
F
PER
a. Fixed Formula b. Variable Formula
Baud_Rate
=
6
F
PER
TB8
SCON.3
IBRG
CLOCK
RXD
TXDSBUF Tx SR
Rx SR
SM1
SCON.6
SM0
SCON.7
Mode Decoder
M3 M2 M1 M0
RI
SCON.0
TI
SCON.1
Mode & Clock
Controller
SBUF Rx RB8
SCON.2
SM2
SCON.4
T1
CLOCK
PER
CLOCK