PIC16F877ATISLASHML datasheet(96/234 Pages) MICROCHIP

96 / 234 page

PIC16F87XA

DS39582B-page 94

 2003 Microchip Technology Inc.

9.4.5

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>

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 inter-

rupt 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 9-15).

FIGURE 9-15:

SLAVE MODE GENERAL CALL ADDRESS SEQUENCE

(7 OR 10-BIT ADDRESS MODE)

SDA

SCL

SSPIF

BF (SSPSTAT<0>)

SSPOV (SSPCON<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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