Intel 8XC251SA, 8XC251SP, 8XC251SQ, 8XC251SB, Embedded Microcontroller manual Given Address, Saddr

8XC251SA, SB, SP, SQ USER’S MANUAL

Implemented in hardware, automatic address recognition enhances the multiprocessor communi- cation feature by allowing the serial port to examine the address of each incoming command frame. Only when the serial port recognizes its own address does the receiver set the RI bit in the SCON register to generate an interrupt. This ensures that the CPU is not interrupted by command frames addressed to other devices.

If desired, you may enable the automatic address recognition feature in mode 1. In this configu- ration, the stop bit takes the place of the ninth data bit. The RI bit is set only when the received command frame address matches the device’s address and is terminated by a valid stop bit.

NOTE

The multiprocessor communication and automatic address recognition features cannot be enabled in mode 0 (i.e., setting the SM2 bit in the SCON register in mode 0 has no effect).

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

10.5.1 Given Address

Each device has an individual address that is specified in the SADDR register; the SADEN reg- ister is a mask byte that contains don't-care bits (defined by zeros) to form the device’s given ad- dress. These 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. Note that to address a device by its individual address, the SADEN mask byte must be 1111 1111.

SADDR = 0101 0110

SADEN = 1111 1100

Given = 0101 01XX

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

Slave A:	SADDR	=	1111	0001	Slave C:	SADDR	=	1111	0010
	SADEN	=	1111	1010		SADEN	=	1111	1101
	Given	=	1111	0X0X		Given	=	1111	00X1
Slave B:	SADDR	=	1111	0011
	SADEN	=	1111	1001
	Given	=	1111	0XX1

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