41594B datasheet(240/372 Pages) MICROCHIP

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PIC12LF1840T48A

DS41594B-page 240

Preliminary

 2011-2012 Microchip Technology Inc.

25.5.8 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 device. 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 a reserved address in the

I2C protocol, defined as address 0x00. When the

GCEN bit of the SSP1CON2 register is set, the slave

module will automatically ACK the reception of this

address, regardless of the value stored in SSP1ADD.

After the slave clocks in an address of all zeros with

the R/W bit clear, an interrupt is generated and slave

software

can

read

SSP1BUF

and

respond.

Figure 25-23

shows

general

call

reception

sequence.

In 10-bit Address mode, the UA bit will not be set on

the reception of the general call address. The slave

will prepare to receive the second byte as data, just as

it would in 7-bit mode.

If the AHEN bit of the SSP1CON3 register is set, just

as with any other address reception, the slave hard-

ware will stretch the clock after the 8th falling edge of

SCL. The slave must then set its ACKDT value and

release the clock with communication progressing as it

would normally.

FIGURE 25-24:

SLAVE MODE GENERAL CALL ADDRESS SEQUENCE

25.5.9

SSP1 MASK REGISTER

An SSP1 Mask (SSP1MSK) register (Register 25-5) is

available in I2C Slave mode as a mask for the value

held in the SSP1SR register during an address

comparison operation. A zero (‘0’) bit in the SSP1MSK

of the received address a “don’t care.”

This register is reset to all ‘1’s upon any Reset

condition and, therefore, has no effect on standard

SSP1 operation until written with a mask value.

The SSP1 Mask register is active during:

• 7-bit Address mode: address compare of A<7:1>.

• 10-bit Address mode: address compare of A<7:0>

only. The SSP1 mask has no effect during the

reception of the first (high) byte of the address.

SDA

SCL

SSP1IF

BF (SSP1STAT<0>)

Cleared by software

SSP1BUF is read

R/W = 0

ACK

General Call Address

Address is compared to General Call Address

Receiving Data

ACK

after ACK, set interrupt

GCEN (SSP1CON2<7>)

’1’

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