Datasheet

PIC18F85J90 FAMILY
DS39770C-page 206  2010 Microchip Technology Inc.
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
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 17-2).
The I
2
C Slave behaves the same way whether address
masking is used or not. However, when address
masking is used, the I
2
C slave can Acknowledge
multiple addresses and cause interrupts. When this
occurs, it is necessary to determine which address
caused the interrupt by checking SSPBUF.
In 7-Bit Address mode, address mask bits, ADMSK<5:1>
(SSPCON<5:1>), mask the corresponding address bits
in the SSPADD register. For any ADMSK bits that are set
(ADMSK<n> = 1), the corresponding address bit is
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, the ADMSK<5:2> bits mask
the corresponding address bits in the SSPADD regis-
ter. 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 correspond-
ing 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 17-2: 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