PIC18F23K22-ESLASHML datasheet(251/496 Pages) MICROCHIP

251 / 496 page

 2010 Microchip Technology Inc.

Preliminary

DS41412C-page 251

PIC18(L)F2X/4XK22

15.6.13.2

Bus Collision During a Repeated

Start Condition

During a Repeated Start condition, a bus collision

occurs if:

A low level is sampled on SDAx when SCLx

goes from low level to high level.

SCLx goes low before SDAx is asserted low,

indicating that another master is attempting to

transmit a data ‘1’.

When the user releases SDAx and the pin is allowed to

float high, the BRG is loaded with SSPxADD and

counts down to zero. The SCLx pin is then deasserted

and when sampled high, the SDAx pin is sampled.

If SDAx is low, a bus collision has occurred (i.e., another

master is attempting to transmit a data ‘0’, Figure 15-35).

If SDAx is sampled high, the BRG is reloaded and

begins counting. If SDAx goes from high-to-low before

the BRG times out, no bus collision occurs because no

two masters can assert SDAx at exactly the same time.

If SCLx goes from high-to-low before the BRG times

out and SDAx has not already been asserted, a bus

collision occurs. In this case, another master is

attempting to transmit a data ‘1’ during the Repeated

Start condition, see Figure 15-36.

If, at the end of the BRG time-out, both SCLx and SDAx

are still high, the SDAx pin is driven low and the BRG

is reloaded and begins counting. At the end of the

count, regardless of the status of the SCLx pin, the

SCLx pin is driven low and the Repeated Start

condition is complete.

FIGURE 15-36:

BUS COLLISION DURING A REPEATED START CONDITION (CASE 1)

FIGURE 15-37:

BUS COLLISION DURING REPEATED START CONDITION (CASE 2)

SDAx

SCLx

RSEN

BCLxIF

SSPxIF

Sample SDAx when SCLx goes high.

If SDAx = 0, set BCLxIF and release SDAx and SCLx.

Cleared by software

’0’

SDAx

SCLx

BCLxIF

RSEN

SSPxIF

Interrupt cleared

by software

SCLx goes low before SDAx,

set BCLxIF. Release SDAx and SCLx.

TBRG

’0’

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