AT89C5122 ATMEL [ATMEL Corporation], AT89C5122 Datasheet - Page 131

• Manufacturer Part Number: AT89C5122
• Description: MICROCONTROLLER WITH USB AND SMART CARD READER INTERFACES
• Manufacturer: ATMEL [ATMEL Corporation]

Baud Rate Selection (Mode 0)
Asynchronous Modes
(Modes 1, 2 and 3)
Mode 1
4202D–SCR–06/05
CLOCK
CLOCK
IBRG
CK_
T1
SI
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)
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 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.
Baud_Rate =
CLOCK
IBRG
a. Fixed Formula
CK_
SI
SCON.4
SM2
SCON.6
M3 M2 M1 M0
SM1
Mode Decoder
Mode & Clock
F
CK_SI
Controller
/ 6
6
SCON.1
TI
SCON.7
SM0
BDRCON.0
M0SRC
SCON.0
RI
0
1
To Serial Port
Baud_Rate =
BRL = 256 -
SCON.3
TB8
SBUF Tx SR
SBUF Rx
b. Variable Formula
Rx SR
6
6
(1-SPD)
(1-SPD)
2
2
SMOD1
SMOD1
⋅ 32 ⋅ Baud_Rate
⋅ 32 ⋅ (256 -BRL)
SCON.2
⋅
⋅
RB8
F
F
CK_SI
CK_SI
TXD
RXD
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