AT83SND1CXXX-ROTIL datasheet(140/212 Pages) ATMEL

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4109J–8051–10/06

AT8xC51SND1C

17.6

Automatic Address Recognition

The automatic address recognition feature is enabled when the multiprocessor communication

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

Implemented in hardware, automatic address recognition enhances the multiprocessor commu-

nication feature by allowing the Serial Port to examine the address of each incoming command

frame. Only when the Serial Port recognizes its own address, the receiver sets RI bit in SCON

frames addressed to other devices.

If desired, the automatic address recognition feature in mode 1 may be enabled. In this configu-

ration, 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 terminated by a valid stop bit.

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

cast 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).

17.6.1

Given Address

Each device has an individual address that is specified in 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:

SADDR = 0101 0110b

SADEN = 1111 1100b

Given = 0101 01XXb

The following is an example of how to use given addresses to address different slaves:

Slave A:SADDR = 1111 0001b

SADEN = 1111 1010b

Given = 1111 0X0Xb

Slave B:SADDR = 1111 0011b

SADEN = 1111 1001b

Given = 1111 0XX1b

Slave C:SADDR = 1111 0011b

SADEN = 1111 1101b

Given = 1111 00X1b

The SADEN Byte is selected so that each slave may be addressed separately.

For slave A, bit 0 (the LSB) is a don’t-care bit; for slaves B and C, bit 0 is a 1. To communicate

with slave A only, the master must send an address where bit 0 is clear (e.g. 1111 0000B).

For slave A, bit 1 is a 0; for slaves B and C, bit 1 is a don’t care bit. To communicate with slaves

A and B, but not slave C, the master must send an address with bits 0 and 1 both set (e.g.

1111 0011B

To communicate with slaves A, B and C, the master must send an address with bit 0 set, bit 1

clear, and bit 2 clear (e.g. 1111 0001B).

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