PIC16F7X7
10.4.17.2
Bus Collision During a Repeated
Start Condition
During a Repeated Start condition, a bus collision
occurs if:
a)
b)
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’.
If SDA is low, a bus collision has occurred (i.e., another
master is attempting to transmit a data ‘0’, see
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.
When the user deasserts 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 deasserted and
when sampled high, the SDA pin is sampled.
FIGURE 10-29:
SDA
BUS COLLISION DURING A REPEATED START CONDITION (CASE 1)
SCL
Sample SDA when SCL goes high.
If SDA =
0,
set BCLIF and release SDA and SCL.
RSEN
BCLIF
Cleared in software
‘0’
‘0’
S
SSPIF
FIGURE 10-30:
BUS COLLISION DURING A REPEATED START CONDITION (CASE 2)
T
BRG
T
BRG
SDA
SCL
SCL goes low before SDA,
set BCLIF. Release SDA and SCL.
Interrupt cleared
in software
RSEN
S
SSPIF
‘0’
BCLIF
DS30498C-page 130
2004 Microchip Technology Inc.
MICROCHIP [ MICROCHIP TECHNOLOGY ]
