PIC18F2610-ESLASHML datasheet(174/376 Pages) MICROCHIP

174 / 376 page

PIC18F2X1X/4X1X

DS39636D-page 176

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 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,

theory,

respond

with

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)

is enabled

(SSPCON2<7> set). Following a Start bit detect, 8 bits

are shifted into the SSPSR and the address is

compared against the 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 bit is set (eighth

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

SSPIF interrupt flag bit is set.

When the interrupt is serviced, the source for the

interrupt can be checked by reading the contents of the

SSPBUF. The value can be used to determine if the

address was device specific or a general call address.

In 10-Bit Address 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 the GCEN bit 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 16-15).

FIGURE 16-15:

SLAVE MODE GENERAL CALL ADDRESS SEQUENCE

(7 OR 10-BIT ADDRESS 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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