AT89C51CC02CA-RATUM datasheet(52/156 Pages) ATMEL

52 / 156 page

AT/T89C51CC02

4126J–CAN–05/06

Figure 22. UART Timing in Mode 1

Figure 23. UART Timing in Modes 2 and 3

Automatic Address

Recognition

The automatic address recognition feature is enabled when the multiprocessor commu-

nication feature is enabled (SM2 bit in SCON register is set).

Implemented in the hardware, automatic address recognition enhances the multiproces-

sor communication feature by allowing the serial port to examine the address of each

incoming command frame. Only when the serial port recognizes its own address will the

receiver set the RI bit in the SCON register to generate an interrupt. This ensures that

the CPU is not interrupted by command frames addressed to other devices.

If necessary, the user can enable the automatic address recognition feature in mode 1.

In this configuration, the stop bit takes the place of the ninth data bit. bit RI is set only

when the received command frame address matches the device’s address and is termi-

nated by a valid stop bit.

To support automatic address recognition, a device is identified by a given address and

a broadcast address.

Note:

The multiprocessor communication and automatic address recognition features cannot

be enabled in mode 0 (i.e. setting SM2 bit in SCON register in mode 0 has no effect).

Given Address

Each device has an individual address that is specified in the SADDR register; the

SADEN register is a mask byte that contains don’t-care bits (defined by zeros) to form

the device’s given address. The don’t-care bits provide the flexibility to address one or

more slaves at a time. The following example illustrates how a given address is formed.

To address a device by its individual address, the SADEN mask byte must be 1111

1111b

For example:

SADDR0101 0110b

SADEN1111 1100b

Given0101 01XXb

Data Byte

SMOD0 = x

Stop

bit

Start

bit

RXD

SMOD0 = 1

SMOD0 = 0

Data Byte

Ninth

bit

Stop

bit

Start

bit

RXD

SMOD0 = 1

AT89C51CC02CA-RATUM 数据表(PDF) 52 Page - ATMEL Corporation

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