AT80SND1C-ROTIL datasheet(137/210 Pages) ATMEL

137 / 210 page

137

AT8xC51SND1C

4109E–8051–06/03

Asynchronous Modes

(Modes 1, 2 and 3)

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

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

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

tively, you can use the ninth bit can be used as a command/data flag.

Figure 103. Data Frame Format (Modes 2 and 3)

Transmission (Modes 1, 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.

Reception (Modes 1, 2 and 3)

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.

TB8

SCON.3

IBRG

CLOCK

RXD

TXD

SBUF Tx SR

Rx SR

SM1

SCON.6

SM0

SCON.7

Mode Decoder

M3 M2 M1 M0

SCON.0

SCON.1

Mode & Clock

Controller

SBUF Rx

RB8

SCON.2

SM2

SCON.4

CLOCK

PER

CLOCK

Mode 1

Start bit

8-bit data

Stop bit

Start bit

9-bit data

Stop bit

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