AT89C5132-ROTIL datasheet(111/181 Pages) ATMEL

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111

4173D–USB–02/06

AT89C5132

18.4

Asynchronous Modes (Modes 1, 2 and 3)

The Serial Port has one 8-bit and two 9-bit asynchronous modes of operation. Figure 18-8

shows the Serial Port block diagram in asynchronous modes.

Figure 18-8. Serial I/O Port Block Diagram (Modes 1, 2 and 3)

18.4.0.1

Mode 1

Mode 1 is a full-duplex, asynchronous mode. The data frame (see Figure 18-9) 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 data is received, the stop bit is read in the RB8 bit in SCON

Figure 18-9. Data Frame Format (Mode 1)

18.4.0.2

Modes 2 and 3

Modes 2 and 3 are full-duplex, asynchronous modes. The data frame (see Figure 18-10) con-

sists 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. Alternatively, the ninth bit can

be used as a command/data flag.

Figure 18-10. Data Frame Format (Modes 2 and 3)

18.4.1

Transmission

(Modes 1, 2 and 3)

To initiate a transmission, write to SCON register, setting SM0 and SM1 Bits according to

Table 89, and setting the ninth bit by writing to TB8 bit. Then, writing the byte to be transmitted to

SBUF register starts the transmission.

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

AT89C5132-ROTIL Datasheet(PDF) 111 Page - ATMEL Corporation

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