AT89C5132-ROTIL datasheet(115/181 Pages) ATMEL

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4173D–USB–02/06

AT89C5132

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).

18.6.2

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 | SADEN)=1111 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:

SADDR = 1111 0001b

SADEN = 1111 1010b

Given = 1111 1X11b,

Slave B:

SADDR = 1111 0011b

SADEN = 1111 1001b

Given = 1111 1X11b,

Slave C:

SADDR = 1111 0010b

SADEN = 1111 1101b

Given = 1111 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 the address FFh.

To communicate with slaves A and B, but not slave C, the master must send the address FBh.

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