AT83SND2CMP3 datasheet(74/97 Pages) ATMEL

74 / 97 page

AT83SND2CMP3

7524B–MP3–05/06

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 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 | 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.

Reset Address

On reset, the SADDR and SADEN registers are initialized to 00h, i.e. the given and

broadcast addresses are XXXX XXXXb (all don’t care bits). This ensures that the Serial

Port is backwards compatible with the 80C51 microcontrollers that do not support auto-

matic address recognition.

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