AT83C51SND1C_03 ATMEL [ATMEL Corporation], AT83C51SND1C_03 Datasheet - Page 137

• Manufacturer Part Number: AT83C51SND1C_03
• Description: Single-Chip Flash Microcontroller with MP3 Decoder and Human Interface
• Manufacturer: ATMEL [ATMEL Corporation]

Transmission (Modes 1, 2
and 3)
Reception (Modes 1, 2 and 3)
Asynchronous Modes
(Modes 1, 2 and 3)
Mode 1
Modes 2 and 3
4109E–8051–06/03
The Serial Port has one 8-bit and 2 9-bit asynchronous modes of operation. Figure 101
shows the Serial Port block diagram in such asynchronous modes.
Figure 101. Serial I/O Port Block Diagram (Modes 1, 2 and 3)
Mode 1 is a full-duplex, asynchronous mode. The data frame (see Figure 102) 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.
Figure 102. Data Frame Format (Mode 1)
Modes 2 and 3 are full-duplex, asynchronous modes. The data frame (see Figure 103)
consists of 11 bits: one start bit, eight data bits (transmitted and received LSB first), one
programmable ninth data bit and one stop bit. Serial data is transmitted on the TXD pin
and received on the RXD pin. On receive, the ninth bit is read from RB8 bit in SCON
register. On transmit, the ninth data bit is written to TB8 bit in SCON register. Alterna-
tively, you can use the ninth bit can be used as a command/data flag.
Figure 103. Data Frame Format (Modes 2 and 3)
To initiate a transmission, write to SCON register, set the SM0 and SM1 bits according
to Table 123, and set the ninth bit by writing to TB8 bit. Then, writing the Byte to be
transmitted to SBUF register starts the transmission.
To prepare for reception, write to SCON register, set the SM0 and SM1 bits according to
Table 123, and set the REN bit. The actual reception is then initiated by a detected high-
to-low transition on the RXD pin.
Mode 1
CLOCK
CLOCK
CLOCK
IBRG
PER
T1
Start bit
Start bit
SCON.4
SM2
D0
SCON.6
M3 M2 M1 M0
SM1
Mode Decoder
Mode & Clock
D0
Controller
D1
SCON.1
TI
D1
SCON.7
D2
SM0
SCON.0
D2
RI
D3
9-bit data
D3
8-bit data
D4
D4
D5
D5
SBUF Tx SR
AT8xC51SND1C
SBUF Rx
D6
Rx SR
SCON.3
TB8
D6
D7
D7
D8
SCON.2
Stop bit
RB8
Stop bit
TXD
RXD
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