PIC17C752-08SLASHCL datasheet(147/328 Pages) MICROCHIP

147 / 328 page

DS30289A-page 147

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

SCL

SSPIF

BF (SSPSTAT<0>)

SSPOV (SSPCON1<6>)

Cleared in software

SSPBUF is read

R/W = 0

ACK

General Call Address

Address is compared to General Call Address

GCEN (SSPCON2<7>)

Receiving data

ACK

after ACK, set interrupt

'0'

'1'

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