Intel 8XC251SP, 8XC251SA, 8XC251SQ, 8XC251SB manual Broadcast Address, Saddr or Saden

SERIAL I/O PORT

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 0000).

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 B and C, but not Slave A, the master must send an address with bits 0 and 1 both set (e.g., 1111 0011).

For Slaves A and B, bit 2 is a don’t-care bit; for Slave C, bit 2 is a 0. To communicate with Slaves A and B, but not Slave C, the master must send an address with bit 0 set, bit 1 clear, and bit 2 set (e.g., 1111 0101).

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 0001).

10.5.2 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 0110
SADEN	=	1111 1100
(SADDR) OR (SADEN)	=	1111 111X

The use of don't-care bits provides flexibility in defining the broadcast address, however, in most applications, a broadcast address is 0FFH.

The following is an example of using broadcast addresses:

Slave A:	SADDR	=	1111 0001		Slave C:	SADDR	=	1111 0010
	SADEN	=	1111 1010			SADEN	=	1111 1101
	Broadcast	=	1111	1X11		Broadcast	=	1111 1111
Slave B:	SADDR	=	1111	0011
	SADEN	=	1111 1001
	Broadcast	=	1111	1X11

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 an address FBH.

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