Datasheet

PIC16F87X
DS30292C-page 76  2001 Microchip Technology Inc.
FIGURE 9-7: I
2
C WAVEFORMS FOR TRANSMISSION (7-BIT ADDRESS)
9.2.2 GENERAL CALL ADDRESS
SUPPORT
The addressing procedure for the I
2
C 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 I
2
C 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. It is also compared to the general call
address and fixed in hardware.
If the general call address matches, the SSPSR is
transferred 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 inter-
rupt can be checked by reading the contents of the
SSPBUF to determine if the address was device spe-
cific, 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 config-
ured 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 9-8).
FIGURE 9-8: SLAVE MODE GENERAL CALL ADDRESS SEQUENCE (7 OR 10-BIT MODE)
SDA
SCL
SSPIF
BF (SSPSTAT<0>)
CKP (SSPCON<4>)
A7 A6 A5 A4 A3 A2 A1
ACK
D7 D6 D5 D4 D3 D2 D1 D0
Not ACK
Transmitting Data
R/W
= 1
Receiving Address
123456789 123456789
P
Cleared in software
SSPBUF is written in software
From SSP Interrupt
Service Routine
Set bit after writing to SSPBUF
S
Data in
sampled
SCL held low
while CPU
responds to SSPIF
(the SSPBUF must be written to,
before the CKP bit can be set)
R/W
= 0
SDA
SCL
S
SSPIF
BF
SSPOV
Cleared in software
SSPBUF is read
R/W
= 0
ACK
General Call Address
Address is compared to General Call Address
GCEN
Receiving data
ACK
123456789123456789
D7 D6 D5 D4 D3 D2 D1 D0
after ACK, set interrupt flag
’0’
’1’
(SSPSTAT<0>)
(SSPCON<6>)
(SSPCON2<7>)