Microchip Technology DM183037 Data Sheet
PIC18F97J94 FAMILY
DS30575A-page 408
2012 Microchip Technology Inc.
20.5.20.2
Bus Collision During a Repeated
Start Condition
Start Condition
During a Repeated Start condition, a bus collision
occurs if:
a)
occurs if:
a)
A low level is sampled on SDAx when SCLx
goes from a low level to a high level.
goes from a low level to a high level.
b)
SCLx goes low before SDAx is asserted low,
indicating that another master is attempting to
transmit a data ‘1’.
indicating that another master is attempting to
transmit a data ‘1’.
When the user deasserts SDAx and the pin is allowed
to float high, the BRG is loaded with SSPxADD<6:0>
and counts down to 0. The SCLx pin is then deasserted
and when sampled high, the SDAx pin is sampled.
to float high, the BRG is loaded with SSPxADD<6:0>
and counts down to 0. The SCLx pin is then deasserted
and when sampled high, the SDAx pin is sampled.
If SDAx is low, a bus collision has occurred (i.e., another
master is attempting to transmit a data ‘0’,
master is attempting to transmit a data ‘0’,
).
If SDAx is sampled high, the BRG is reloaded and
begins counting. If SDAx goes from high-to-low before
the BRG times out, no bus collision occurs because no
two masters can assert SDAx at exactly the same time.
If SCLx goes from high-to-low before the BRG times
out and SDAx 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
begins counting. If SDAx goes from high-to-low before
the BRG times out, no bus collision occurs because no
two masters can assert SDAx at exactly the same time.
If SCLx goes from high-to-low before the BRG times
out and SDAx 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
If, at the end of the BRG time-out, both SCLx and SDAx
are still high, the SDAx pin is driven low and the BRG
is reloaded and begins counting. At the end of the
count, regardless of the status of the SCLx pin, the
SCLx pin is driven low and the Repeated Start
condition is complete.
are still high, the SDAx pin is driven low and the BRG
is reloaded and begins counting. At the end of the
count, regardless of the status of the SCLx pin, the
SCLx pin is driven low and the Repeated Start
condition is complete.
FIGURE 20-31:
BUS COLLISION DURING A REPEATED START CONDITION (CASE 1)
FIGURE 20-32:
BUS COLLISION DURING REPEATED START CONDITION (CASE 2)
SDAx
SCLx
RSEN
BCLxIF
S
SSPxIF
Sample SDAx when SCLx goes High,
If SDAx = 0, Set BCLxIF and Release SDAx and SCLx
If SDAx = 0, Set BCLxIF and Release SDAx and SCLx
Cleared in Software
‘0’
‘0’
SDAx
SCLx
BCLxIF
RSEN
S
SSPxIF
Interrupt Cleared
in Software
in Software
SCLx goes Low Before SDAx,
Set BCLxIF, Release SDAx and SCLx
Set BCLxIF, Release SDAx and SCLx
T
BRG
T
BRG
‘0’