PIC16 datasheet(227/418 Pages) MICROCHIP

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DS40001609C-page 227

PIC16(L)F1508/9

21.6.13.3

Bus Collision During a Stop

Condition

Bus collision occurs during a Stop condition if:

After the SDAx pin has been deasserted and

allowed to float high, SDAx is sampled low after

the BRG has timed out (Case 1).

After the SCLx pin is deasserted, SCLx is

sampled low before SDAx goes high (Case 2).

The Stop condition begins with SDAx asserted low.

When SDAx is sampled low, the SCLx pin is allowed to

float. When the pin is sampled high (clock arbitration),

the Baud Rate Generator is loaded with SSPxADD and

counts down to 0. After the BRG times out, SDAx is

sampled. If SDAx is sampled low, a bus collision has

occurred. This is due to another master attempting to

drive a data ‘0’ (Figure 21-38). If the SCLx pin is

sampled low before SDAx is allowed to float high, a bus

collision occurs. This is another case of another master

attempting to drive a data ‘0’ (Figure 21-39).

FIGURE 21-38:

BUS COLLISION DURING A STOP CONDITION (CASE 1)

FIGURE 21-39:

BUS COLLISION DURING A STOP CONDITION (CASE 2)

SDAx

SCLx

BCLxIF

PEN

SSPxIF

TBRG

SDAx asserted low

SDAx sampled

low after TBRG,

set BCLxIF

‘0’

SDAx

SCLx

BCLxIF

PEN

SSPxIF

TBRG

Assert SDAx

SCLx goes low before SDAx goes high,

set BCLxIF

‘0’

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