PIC18F44J10 datasheet(177/368 Pages) MICROCHIP

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DS39682E-page 175

PIC18F45J10 FAMILY

16.4.5

GENERAL CALL ADDRESS

SUPPORT

The addressing procedure for the I2C bus is such that

the first byte after the Start condition usually

determines 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

General

Call

Enable

bit,

GCEN,

enabled

(SSPxCON2<7> set). Following a Start bit detect, 8 bits

are shifted into the SSPxSR and the address is

compared against the SSPxADD. It is also compared to

the general call address and fixed in hardware.

If the general call address matches, the SSPxSR is

transferred to the SSPxBUF, the BF flag bit is set

(eighth bit) and on the falling edge of the ninth bit (ACK

bit), the SSPxIF interrupt flag bit is set.

When the interrupt is serviced, the source for the

interrupt can be checked by reading the contents of the

SSPxBUF. The value can be used to determine if the

address was device-specific or a general call address.

In 10-bit mode, the SSPxADD is required to be updated

for the second half of the address to match and the UA

bit is set (SSPxSTAT<1>). If the general call address is

sampled when the GCEN bit is set, while the slave is

configured in 10-Bit Addressing 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 16-15).

FIGURE 16-15:

SLAVE MODE GENERAL CALL ADDRESS SEQUENCE

(7 OR 10-BIT ADDRESSING MODE)

SDAx

SCLx

SSPxIF

BF (SSPxSTAT<0>)

SSPOV (SSPxCON1<6>)

Cleared in software

SSPxBUF is read

R/W = 0

ACK

General Call Address

Address is compared to General Call Address

GCEN (SSPxCON2<7>)

Receiving Data

ACK

after ACK, set interrupt

‘0’

‘1’

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