PIC18F4550ESOSQTP datasheet(210/430 Pages) MICROCHIP

210 / 430 page

PIC18F2455/2550/4455/4550

DS39632D-page 208

Preliminary

19.4.3.2

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 mode and up to 63

addresses in 10-bit mode (see Example 19-2).

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 SSPBUF.

7-Bit

Address

mode,

address

mask

bits

ADMSK<5:1> (SSPCON2<5:1>) mask the corre-

sponding address bits in the SSPADD register. For any

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

corresponding

address

bit

ignored

(SSPADD<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 Address mode, bits ADMSK<5:2> mask the

corresponding address bits in the SSPADD register. In

addition, ADMSK1 simultaneously masks the two LSbs

of the address (SSPADD<1:0>). For any ADMSK bits

that are active (ADMSK<n> = 1), the corresponding

address bit is ignored (SSPADD<n> = x). Also note

that although in 10-Bit Addressing mode, the upper

address bits reuse part of the SSPADD register bits, the

address mask bits do not interact with those bits. They

only affect the lower address bits.

EXAMPLE 19-2:

ADDRESS MASKING EXAMPLES

Note 1: ADMSK1 masks the two Least Significant

bits of the address.

2: The two Most Significant bits of the

address are not affected by address

masking.

7-bit addressing:

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

ADMSK<5:1>

= 00111

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

10-bit addressing:

SSPADD<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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