PIC18F44J10-ISLASHSOSQTP datasheet(192/368 Pages) MICROCHIP

192 / 368 page

PIC18F45J10 FAMILY

DS39682E-page 190

16.4.17.2

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 deasserts SDAx and the pin is allowed

to float high, the BRG is loaded with SSPxADD<6:0>

and counts down to 0. 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’, see

Figure 16-29). 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 16-30).

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 16-29:

BUS COLLISION DURING A REPEATED START CONDITION (CASE 1)

FIGURE 16-30:

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 in software

‘0’

SDAx

SCLx

BCLxIF

RSEN

SSPxIF

Interrupt cleared

in software

SCLx goes low before SDAx,

set BCLxIF. Release SDAx and SCLx.

TBRG

‘0’

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