PIC18F4520ESLASHMLQTP datasheet(201/390 Pages) MICROCHIP

201 / 390 page

 2004 Microchip Technology Inc.

Preliminary

DS39631A-page 199

PIC18F2420/2520/4420/4520

17.4.17.3

Bus Collision During a Stop

Condition

Bus collision occurs during a Stop condition if:

After the SDA pin has been deasserted and

allowed to float high, SDA is sampled low after

the BRG has timed out.

After the SCL pin is deasserted, SCL is sampled

low before SDA goes high.

The Stop condition begins with SDA asserted low.

When SDA is sampled low, the SCL pin is allowed to

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

the Baud Rate Generator is loaded with SSPADD<6:0>

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

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

occurred. This is due to another master attempting to

drive a data ‘0’ (Figure 17-31). If the SCL pin is

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

collision occurs. This is another case of another master

attempting to drive a data ‘0’ (Figure 17-32).

FIGURE 17-31:

BUS COLLISION DURING A STOP CONDITION (CASE 1)

FIGURE 17-32:

BUS COLLISION DURING A STOP CONDITION (CASE 2)

SDA

SCL

BCLIF

PEN

SSPIF

TBRG

SDA asserted low

SDA sampled

low after TBRG,

set BCLIF

‘0’

SDA

SCL

BCLIF

PEN

SSPIF

TBRG

Assert SDA

SCL goes low before SDA goes high,

set BCLIF

‘0’

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