Microchip Technology MCP1631RD-MCC2 Data Sheet

DS41291G-page 210

 2006-2012 Microchip Technology Inc.

13.4.16.2

Bus Collision During a Repeated 
Start Condition

During a Repeated Start condition, a bus collision
occurs if: 
a)

A low level is sampled on SDA when SCL goes
from low level to high level.

b)

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’, see

). 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
(

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. 

SDA

SCL

RSEN

BCLIF

S

SSPIF

Sample SDA when SCL goes high,
If SDA = 0, set BCLIF and release SDA and SCL

Cleared in software

‘0’

‘0’

SDA

SCL

BCLIF

RSEN

S

SSPIF

Interrupt cleared
in software

SCL goes low before SDA,
Set BCLIF, release SDA and SCL

T

BRG

T

BRG

‘

0

’