MCP19124 datasheet(177/236 Pages) MICROCHIP

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 2016 Microchip Technology Inc.

DS20005619A-page 177

MCP19124/5

28.4.9

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 in the SSPCON2 register is set, the slave

module will automatically ACK the reception of this

address regardless of the value stored in SSPADD.

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 28-16

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 in 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 28-16:

SLAVE MODE GENERAL CALL ADDRESS SEQUENCE

28.4.10

SSPMSK1 REGISTER

An SSP Mask (SSPMSK1) register is available in I2C

Slave mode as a mask for the value held in the

SSPSR register during an address comparison

operation. A zero (‘0’) bit in the SSPMSK1 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 SSPMSK1 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 (SSPSTAT0)

Cleared by software

SSPBUF is read

R/W = 0

ACK

General Call Address

Receiving Data

ACK

D7 D6 D5 D4 D3 D2 D1 D0

GCEN (SSPCON2<7>)

‘1’

Address is compared to General Call Address

after ACK, set interrupt

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