41594B datasheet(254/372 Pages) MICROCHIP

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PIC12LF1840T48A

DS41594B-page 254

Preliminary

 2011-2012 Microchip Technology Inc.

25.6.13.2

Bus Collision During a Repeated

Start Condition

During a Repeated Start condition, a bus collision

occurs if:

A low level is sampled on SDA when SCL goes

from low level to high level.

SCL goes low before SDA is asserted low,

indicating that another master is attempting to

transmit a data ‘1’.

When the user releases SDA and the pin is allowed to

float high, the BRG is loaded with SSP1ADD and

counts down to zero. The SCL pin is then deasserted

and when sampled high, the SDA pin is sampled.

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

master is attempting to transmit a data ‘0’, Figure 25-35).

If SDA is sampled high, the BRG is reloaded and begins

counting. If SDA goes from high-to-low before the BRG

times out, no bus collision occurs because no two

masters can assert SDA at exactly the same time.

If SCL goes from high-to-low before the BRG times out

and SDA 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 25-36.

If, at the end of the BRG time-out, both SCL and SDA

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

reloaded and begins counting. At the end of the count,

regardless of the status of the SCL pin, the SCL pin is

driven low and the Repeated Start condition is

complete.

FIGURE 25-36:

BUS COLLISION DURING A REPEATED START CONDITION (CASE 1)

FIGURE 25-37:

BUS COLLISION DURING REPEATED START CONDITION (CASE 2)

SDA

SCL

RSEN

BCL1IF

SSP1IF

Sample SDA when SCL goes high.

If SDA = 0, set BCL1IF and release SDA and SCL.

Cleared by software

’0’

SDA

SCL

BCL1IF

RSEN

SSP1IF

Interrupt cleared

by software

SCL goes low before SDA,

set BCL1IF. Release SDA and SCL.

TBRG

’0’

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