DM163006 datasheet(162/320 Pages) MICROCHIP

162 / 320 page

PIC18C601/801

DS39541A-page 162

Advance Information

 2001 Microchip Technology Inc.

15.4.2

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 (enabled) when

the General Call Enable (GCEN) bit is set (SSPCON2

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 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 register). If the general call address

is sampled when the GCEN bit is set and 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 15-9).

FIGURE 15-9:

SLAVE MODE GENERAL CALL ADDRESS SEQUENCE (7 OR 10-BIT ADDRESS)

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

’0’

’1’

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