OPTION_REG datasheet(166/222 Pages) MICROCHIP

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MCP19111

DS22331A-page 166

 2013 Microchip Technology Inc.

27.4.9

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 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 SSPCON2 register is set, the slave

module will automatically ACK the reception of this

address, regardless of the value stored in SSPADDx.

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 SSPBUF and respond. Figure 27-16

shows a 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 the 7-bit mode.

If the AHEN bit of the SSPCON3 register is set, just as

with any other address reception, the slave hardware

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 27-16:

SLAVE MODE GENERAL CALL ADDRESS SEQUENCE

27.4.10

SSPMSKX REGISTER

An SSP Mask (SSPMSKx) register (Register 27-6 and

mask for the value held in the SSPSRx register during

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

SSPMSKx register has the effect of making the

corresponding bit 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

SSP operation until written with a mask value.

The SSP 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 SSP mask has no effect during the

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

SDA

SCL

SSPIF

BF (SSPSTAT<0>)

Cleared by software

SSPBUF is read

R/W = 0

ACK

General Call Address

Address is compared to General Call Address

Receiving Data

ACK

D7 D6

D5 D4 D3 D2 D1 D0

after ACK, set interrupt

GCEN (SSPCON2<7>)

’1’

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