PIC17C7XX Datasheet, PDF (147/328 Pages) Microchip Technology – High-Performance 8-Bit CMOS EPROM Microcontrollers with 10-bit A/D

PIC17C7XX
15.2.2 GENERAL CALL ADDRESS SUPPORT
The addressing procedure for the I²C bus is such that
the first byte after the START condition usually deter-
mines which device will be the slave addressed by the
master. The exception is the general call address
which can address all devices. When this address is
used, all devices should, in theory, respond with an
acknowledge.
The general call address is one of eight addresses
reserved for specific purposes by the I²C protocol. It
consists of all 0’s with R/W = 0
The general call address is recognized when the Gen-
eral Call Enable bit (GCEN) is enabled (SSPCON2<7>
is set). Following a start-bit detect, 8-bits are shifted
into SSPSR and the address is compared against
SSPADD, and is also compared to the general call
address, fixed in hardware.
If the general call address matches, the SSPSR is
transfered to the SSPBUF, the BF flag is set (eighth
bit), and on the falling edge of the ninth bit (ACK bit)
the SSPIF flag is set.
When the interrupt is serviced. The source for the
interrupt can be checked by reading the contents of
the SSPBUF to determine if the address was device
specific or a general call address.
In 10-bit mode, the SSPADD is required to be updated
for the second half of the address to match, and the
UA bit is set (SSPSTAT<1>). If the general call
address is sampled when GCEN is set while the slave
is configured in 10-bit address mode, then the second
half of the address is not necessary, the UA bit will not
be set, and the slave will begin receiving data after the
acknowledge (Figure 15-19).
FIGURE 15-19: SLAVE MODE GENERAL CALL ADDRESS SEQUENCE (7 OR 10-BIT MODE)
SDA
General Call Address
Address is compared to General Call Address
after ACK, set interrupt
R/W = 0
Receiving data
ACK
ACK D7 D6 D5 D4 D3 D2 D1 D0
SCL
SSPIF
S
1 2 34 5 6 78 91 2 34 5 6 78 9
BF (SSPSTAT<0>)
SSPOV (SSPCON1<6>)
Cleared in software
SSPBUF is read
'0'
GCEN (SSPCON2<7>)
'1'
© 1998 Microchip Technology Inc.
DS30289A-page 147