PIC18F44J10 datasheet(167/368 Pages) MICROCHIP

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DS39682E-page 165

PIC18F45J10 FAMILY

16.4.3.2

Address Masking

Masking an address bit causes that bit to become a

“don’t care”. When one address bit is masked, two

addresses will be Acknowledged and cause an

interrupt. It is possible to mask more than one address

bit at a time, which makes it possible to Acknowledge

up to 31 addresses in 7-Bit Addressing mode and up to

63 addresses in 10-Bit Addressing mode (see

Example 16-2).

The I2C Slave behaves the same way, whether

address masking is used or not. However, when

address masking is used, the I2C slave can

Acknowledge multiple addresses and cause interrupts.

When this occurs, it is necessary to determine which

address caused the interrupt by checking SSPxBUF.

In 7-Bit Addressing mode, Address Mask bits,

ADMSK<5:1>

(SSPxCON2<5:1>),

mask

the

corresponding address bits in the SSPxADD register. For

any ADMSK bits that are set (ADMSK<n> = 1), the cor-

responding address bit is ignored (SSPxADD<n> = x).

For the module to issue an address Acknowledge, it is

sufficient to match only on addresses that do not have an

active address mask.

In 10-Bit Addressing mode, ADMSK<5:2> bits mask

the corresponding address bits in the SSPxADD regis-

ter. In addition, ADMSK1 simultaneously masks the two

LSbs of the address (SSPxADD<1:0>). For any

ADMSK bits that are active (ADMSK<n> = 1), the cor-

responding address bit is ignored (SSPxADD<n> = x).

Also note that although in 10-Bit Addressing mode, the

upper address bits reuse part of the SSPxADD register

bits, the address mask bits do not interact with those

bits. They only affect the lower address bits.

EXAMPLE 16-2:

ADDRESS MASKING EXAMPLES

Note 1:

ADMSK1 masks the two Least Significant

bits of the address.

The two Most Significant bits of the

address are not affected by address

masking.

7-Bit Addressing:

SSPxADD<7:1>= A0h (1010000) (SSPxADD<0> is assumed to be ‘0’)

ADMSK<5:1> = 00111

Addresses Acknowledged: A0h, A2h, A4h, A6h, A8h, AAh, ACh, AEh

10-Bit Addressing:

SSPxADD<7:0>= A0h (10100000) (the two MSbs of the address are ignored in this example, since they are

not affected by masking)

ADMSK<5:1> = 00111

Addresses Acknowledged: A0h, A1h, A2h, A3h, A4h, A5h, A6h, A7h, A8h, A9h, AAh, ABh, ACh, ADh, AEh, AFh

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