PIC18LF24K Datasheet, PDF (382/594 Pages) –

PIC18(L)F26/45/46K40
26.10.13.2 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 (Case 1).
b) SCL goes low before SDA is asserted low,
indicating that another master is attempting to
transmit a data ‘1’ (Case 2).
When the user releases SDA and the pin is allowed to
float high, the BRG is loaded with SSPxADD and
counts down to zero. The SCL pin is then deasserted
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’, Figure 26-36).
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,
see Figure 26-37.
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.
FIGURE 26-36:
SDA
BUS COLLISION DURING A REPEATED START CONDITION (CASE 1)
SCL
RSEN
Sample SDA when SCL goes high.
If SDA = ⁰, set BCLxIF and release SDA and SCL.
BCLxIF
S
SSPxIF
Cleared by software
’0’
’0’
FIGURE 26-37:
BUS COLLISION DURING REPEATED START CONDITION (CASE 2)
TBRG
TBRG
SDA
SCL
BCLxIF
RSEN
S
SSPxIF
SCL goes low before SDA,
set BCLxIF. Release SDA and SCL.
Interrupt cleared
by software
’0’
 2016 Microchip Technology Inc.
Preliminary
DS40001816C-page 382