PIC18F4520ESLASHMLQTP datasheet(186/390 Pages) MICROCHIP

186 / 390 page

PIC18F2420/2520/4420/4520

DS39631A-page 184

Preliminary

 2004 Microchip Technology Inc.

17.4.5

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 Gen-

eral Call Enable bit, GCEN, is enabled (SSPCON2<7>

is 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 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 17-15).

FIGURE 17-15:

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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