PIC16C770-04SLASHP datasheet(83/200 Pages) MICROCHIP

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PIC16C717/770/771

Advanced Information

DS41120A-page 83

9.2.2

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. It is also compared to the general call

address, 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 9-13).

FIGURE 9-13: SLAVE MODE GENERAL CALL ADDRESS SEQUENCE (7 OR 10-BIT MODE)

SDA

SCL

SSPIF

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

after ACK, set interrupt flag

’0’

’1’

(SSPSTAT<0>)

(SSPCON<6>)

(SSPCON2<7>)

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