PIC18F23K22-ESLASHML datasheet(237/496 Pages) MICROCHIP

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 2010 Microchip Technology Inc.

Preliminary

DS41412C-page 237

PIC18(L)F2X/4XK22

15.5.8

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 SSPxCON2 register is set, the slave

module will automatically ACK the reception of this

address regardless of the value stored in SSPxADD.

After the slave clocks in an address of all zeros with the

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

ware can read SSPxBUF and respond. Figure 15-23

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 7-bit mode.

If the AHEN bit of the SSPxCON3 register is set, just

as with any other address reception, the slave

hardware will stretch the clock after the 8th falling

edge of SCLx. The slave must then set its ACKDT

value and release the clock with communication

progressing as it would normally.

FIGURE 15-24:

SLAVE MODE GENERAL CALL ADDRESS SEQUENCE

15.5.9

SSPx MASK REGISTER

An SSPx Mask (SSPxMSK) register (Register 15-5) is

available in I2C Slave mode as a mask for the value

held in the SSPxSR register during an address

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

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

SSPx operation until written with a mask value.

The SSPx 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 SSPx mask has no effect during the

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

SDAx

SCLx

SSPxIF

BF (SSPxSTAT<0>)

Cleared by software

SSPxBUF is read

R/W = 0

ACK

General Call Address

Address is compared to General Call Address

Receiving Data

ACK

after ACK, set interrupt

GCEN (SSPxCON2<7>)

’1’

PIC18F23K22-E/ML Datasheet(PDF) 237 Page - Microchip Technology

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