PIC17C752-08SLASHP datasheet(163/320 Pages) MICROCHIP

163 / 320 page

Preliminary

DS30264A-page 163

PIC17C75X

15.2.14.2 BUS COLLISION DURING A RESTART

CONDITION

During a RESTART condition, a bus collision occurs if:

A ’0’ is sampled on SDA when SCL goes from ’0’

to ’1’

SCL goes low before SDA is asserted low, indi-

cating that another master is attempting to trans-

mit a data ’1’.

When the user de-asserts SDA and the pin is allowed

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

and counts down to 0.

The SCL pin is then

de-asserted, 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’). If however SDA is sampled high then 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, however, SCL goes from high to low before the

BRG times out and SDA has not already been

asserted, then a bus collision occurs. In this case,

another master is attempting to transmit a data ’1’ dur-

ing the RESTART condition.

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

are still high, the SDA pin is driven low, 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 RESTART condition is com-

plete. (Figure 15-41)

FIGURE 15-41: BUS COLLISION DURING A RESTART CONDITION (CASE 1)

FIGURE 15-42: BUS COLLISION DURING RESTART CONDITION (CASE 2)

SDA

SCL

RSEN

BCLIF

SSPIF

Sample SDA when SCL goes high.

If SDA = 0, set BCLIF and release SDA and SCL

Cleared in software

SDA

SCL

BCLIF

RSEN

SSPIF

Interrupt cleared

in software

SCL goes low before SDA,

Set BCLIF. Release SDA and SCL

TBRG

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