PIC18F4321 datasheet(178/396 Pages) MICROCHIP

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PIC18F4321 FAMILY

DS39689E-page 176

Preliminary

17.4.3.2

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 inter-

rupt. 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

10-bit

Addressing

mode

(see

Example 17-2).

The I2C slave behaves the same way whether address

masking is used or not. However, when address mask-

ing 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 the SSPBUF register.

• 7-bit Address mode

Address mask bits, ADMSK<5:1>, mask the corre-

sponding address bits in the SSPADD register. For any

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

corresponding address bit is ignored (ADD<n> = x). For

the module to issue an address Acknowledge, it is suffi-

cient to match only on addresses that do not have an

active address mask.

• 10-bit Address mode

Address

mask

bits,

ADMSK<5:2>,

mask

the

corresponding address bits in the SSPADD register. In

addition, ADMSK<1> simultaneously masks the two

LSBs of the address, ADD<1:0>. For any ADMSK bits

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

address bit is ignored (ADD<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 17-2:

ADDRESS MASKING

Note 1: ADMSK<1>

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 mode:

SSPADD<7:1> = 1010 0000

ADMSK<5:1> = 00 111

Addresses Acknowledged = 0xA0, 0xA2, 0xA4, 0xA6, 0xA8, 0xAA, 0xAC, 0xAE

10-bit Addressing mode:

SSPADD<7:0> = 1010 0000 (The two MSbs are ignored in this example since they are not affected)

ADMSK<5:1> = 00 111

Addresses Acknowledged = 0xA0, 0xA1, 0xA2, 0xA3, 0xA4, 0xA5, 0xA6, 0xA7, 0xA8, 0xA9, 0xAA, 0xAB,

0xAC, 0xAD, 0xAE, 0xAF

The upper two bits are not affected by the address masking.

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