PIC18F2455_07 Datasheet, PDF (210/430 Pages) Microchip Technology – 28/40/44-Pin, High Performance, Enhanced Flash, USB Microcontrollers with nanoWatt Technology

PIC18F2455/2550/4455/4550
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.
In 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 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, 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.
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.
EXAMPLE 19-2: ADDRESS MASKING EXAMPLES
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
DS39632D-page 208
Preliminary
© 2007 Microchip Technology Inc.