Datasheet

PIC16(L)F1824/8
DS40001419F-page 274  2010-2015 Microchip Technology Inc.
FIGURE 25-35: BRG RESET DUE TO SDA ARBITRATION DURING START CONDITION
25.6.13.2 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.
b) SCL goes low before SDA is asserted low,
indicating that another master is attempting to
transmit a data ‘1’.
When the user releases SDA and the pin is allowed to
float high, the BRG is loaded with SSP1ADD 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 25-36).
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 25-37.
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.
SDA
SCL
SEN
Set S
Less than TBRG
TBRG
SDA = 0, SCL = 1
BCL1IF
S
SSP1IF
S
Interrupts cleared
by software
set SSP1IF
SDA = 0, SCL = 1,
SCL pulled low after BRG
time-out
Set SSP1IF
‘0’
SDA pulled low by other master.
Reset BRG and assert SDA.
Set SEN, enable Start
sequence if SDA = 1, SCL = 1