AT89C5131A-RDTUM datasheet(69/188 Pages) ATMEL

69 / 188 page

4337K–USB–04/08

AT89C5130A/31A-M

15. Serial I/O Port

The serial I/O port in the AT89C5130A/31A-M is compatible with the serial I/O port in the 80C52.

It provides both synchronous and asynchronous communication modes. It operates as an Uni-

versal Asynchronous Receiver and Transmitter (UART) in three full-duplex modes (modes 1, 2

and 3). Asynchronous transmission and reception can occur simultaneously and at different

baud rates.

Serial I/O port includes the following enhancements:

• Framing error detection

• Automatic address recognition

15.1

Framing Error Detection

Framing bit error detection is provided for the three asynchronous modes (modes 1, 2 and 3). To

enable the framing bit error detection feature, set SMOD0 bit in PCON register (see Figure 15-

1).

Figure 15-1. Framing Error Block Diagram

When this feature is enabled, the receiver checks each incoming data frame for a valid stop bit.

An invalid stop bit may result from noise on the serial lines or from simultaneous transmission by

two CPUs. If a valid stop bit is not found, the Framing Error bit (FE) in SCON register (See Table

15-1) bit is set.

Software may examine FE bit after each reception to check for data errors. Once set, only soft-

ware or a reset can clear FE bit. Subsequently received frames with valid stop bits cannot clear

FE bit. When FE feature is enabled, RI rises on stop bit instead of the last data bit (See Figure

15-2 and Figure 15-3).

Figure 15-2. UART Timings in Mode 1

RB8

TB8

REN

SM2

SM1

SM0/FE

IDL

GF0

GF1

POF

SMOD0

SMOD1

To UART Framing Error Control

SM0 to UART Mode Control (SMOD0 = 0)

Set FE Bit if Stop Bit is 0 (framing error) (SMOD0 = 1)

SCON (98h)

PCON (87h)

Data Byte

SMOD0 = X

Stop

Bit

Start

Bit

RXD

SMOD0 = 1

AT89C5131A-RDTUM Datasheet(PDF) 69 Page - ATMEL Corporation

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