AT89C51CC02CA-RATUM datasheet(53/156 Pages) ATMEL

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AT/T89C51CC02

4126J–CAN–05/06

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

Slave A:SADDR1111 0001b

SADEN1111 1010b

Given1111 0X0Xb

Slave B:SADDR1111 0011b

SADEN1111 1001b

Given1111 0XX1b

Slave C:SADDR1111 0011b

SADEN1111 1101b

Given1111 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 com-

municate 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).

Broadcast Address

A broadcast address is formed from the logical OR of the SADDR and SADEN registers

with zeros defined as don’t-care bits, e.g.:

SADDR 0101 0110b

SADEN 1111 1100b

SADDR OR SADEN1111 111Xb

The use of don’t-care bits provides flexibility in defining the broadcast address, however

in most applications, a broadcast address is FFh. The following is an example of using

broadcast addresses:

Slave A:SADDR1111 0001b

SADEN1111 1010b

Given1111 1X11b,

Slave B:SADDR1111 0011b

SADEN1111 1001b

Given1111 1X11B,

Slave C:SADDR=1111 0010b

SADEN1111 1101b

Given1111 1111b

For slaves A and B, bit 2 is a don’t care bit; for slave C, bit 2 is set. To communicate with

all of the slaves, the master must send an address FFh. To communicate with slaves A

and B, but not slave C, the master can send and address FBh.

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