P87LPC779FDH datasheet(53/74 Pages) PHILIPS

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Philips Semiconductors

P87LPC779

CMOS single-chip 8-bit microcontroller

Product data

Rev. 02 — 03 May 2004

53 of 74

9397 750 13213

Using the Automatic Address Recognition feature allows a master to selectively

communicate with one or more slaves by invoking the Given slave address or

addresses. All of the slaves may be contacted by using the Broadcast address. Two

special Function Registers are used to deﬁne the slave’s address, SADDR, and the

address mask, SADEN. SADEN is used to deﬁne which bits in the SADDR are to be

used and which bits are ‘don’t care’. The SADEN mask can be logically ANDed with

the SADDR to create the ‘Given’ address which the master will use for addressing

each of the slaves. Use of the Given address allows multiple slaves to be recognized

while excluding others. The following examples will help to show the versatility of this

scheme:

In the above example SADDR is the same and the SADEN data is used to

differentiate between the two slaves. Slave 0 requires a ‘0’ in bit 0 and it ignores bit 1.

Slave 1 requires a ‘0’ in bit 1 and bit 0 is ignored. A unique address for Slave 0 would

be 1100 0010 since slave 1 requires a ‘0’ in bit 1. A unique address for slave 1 would

be 1100 0001 since a ‘1’ in bit 0 will exclude slave 0. Both slaves can be selected at

the same time by an address which has bit 0 = 0 (for slave 0) and bit 1 = 0 (for

slave 1). Thus, both could be addressed with 1100 0000.

In a more complex system the following could be used to select slaves 1 and 2 while

excluding slave 0:

In the above example the differentiation among the 3 slaves is in the lower 3 address

bits. Slave 0 requires that bit 0 = 0 and it can be uniquely addressed by 1110 0110.

Slave 1 requires that bit 1 = 0 and it can be uniquely addressed by 1110 and 0101.

Slave 2 requires that bit 2 = 0 and its unique address is 1110 0011. To select Slaves 0

and 1 and exclude Slave 2 use address 1110 0100, since it is necessary to make bit

2 = 1 to exclude slave 2. The Broadcast Address for each slave is created by taking

the logical OR of SADDR and SADEN. Zeros in this result are treated as don’t-cares.

In most cases, interpreting the don’t-cares as ones, the broadcast address will be FF

hexadecimal. Upon reset SADDR and SADEN are loaded with 0s. This produces a

given address of all ‘don’t cares’ as well as a Broadcast address of all ‘don’t cares’.

This effectively disables the Automatic Addressing mode and allows the

microcontroller to use standard UART drivers which do not make use of this feature.

Table 41:

Slave 0/1 examples

Example 1

Example 2

Slave 0

SADDR = 1100 0000

Slave 1

SADDR = 1100 0000

SADEN = 1111 1101

SADEN = 1111 1110

Given = 1100 00X0

Given = 1100 000X

Table 42:

Slave 0/1/2 examples

Example 1

Example 2

Example 3

Slave 0

SADDR = 1100 0000

Slave 1

SADDR = 1110 0000

Slave 2

SADDR = 1110 0000

SADEN = 1111 1001

SADEN = 1111 1010

SADEN = 1111 1100

Given = 1100 0XX0

Given = 1110 0X0X

Given = 1110 00XX

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