Rainbow Electronics AT89C5122 - Manual (Page 131)

131
AT8xC5122/23
4202E–SCR–06/06
Baud Rate Selection (Mode 0) In mode 0, baud rate can be either fixed or variable.
As shown in Figure 73, the selection is done using M0SRC bit in BDRCON register.
Figure 74 gives the baud rate calculation formulas for each baud rate source.
Figure 73. Baud Rate Source Selection (Mode 0)
Figure 74. Baud Rate Formulas (Mode 0)
Asynchronous Modes
(Modes 1, 2 and 3) The Serial Port has one 8-bit and two 9-bit asynchronous modes of operation. Figure 75
shows the Serial Port block diagram in such asynchronous modes.
Figure 75. Serial I/O Port Block Diagram (Modes 1, 2 and 3)
Mode 1 Mode 1 is a full-duplex, asynchronous mode. The data frame (see Figure 76) 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
CK_
SI
/ 6
To Serial Port
IBRG
CLOCK
Baud_Rate
=
6 (1-SPD) ⋅ 32 ⋅ (256 -BRL)
2 SMOD1 ⋅
F
CK_SI
BRL = 256 -
6 (1-SPD) ⋅ 32 ⋅ Baud_Rate
2 SMOD1 ⋅
F
CK_SI
a. Fixed Formula b. Variable Formula
Baud_Rate =
6
F
CK_SI
TB8
SCON.3
IBRG
CLOCK
RXD
TXD SBUF 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
CK_
SI