Microchip Technology AC244045 Data Sheet
PIC16(L)F1825/1829
DS41440C-page 284
2010-2012 Microchip Technology Inc.
25.6.13.2
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 low level to high level. (CASE 1)
goes from low level to high level. (CASE 1)
b)
SCLx goes low before SDAx is asserted low,
indicating that another master is attempting to
transmit a data ‘1’. (CASE 2)
indicating that another master is attempting to
transmit a data ‘1’. (CASE 2)
When the user releases SDAx and the pin is allowed to
float high, the BRG is loaded with SSPxADD and
counts down to zero. The SCLx pin is then deasserted
and when sampled high, the SDAx pin is sampled.
float high, the BRG is loaded with SSPxADD and
counts down to zero. 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 (
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 (
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 25-36:
BUS COLLISION DURING A REPEATED START CONDITION (CASE 1)
FIGURE 25-37:
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 by software
‘0’
‘0’
SDAx
SCLx
BCLxIF
RSEN
S
SSPxIF
Interrupt cleared
by software
by software
SCLx goes low before SDAx,
set BCLxIF. Release SDAx and SCLx.
set BCLxIF. Release SDAx and SCLx.
T
BRG
T
BRG
‘0’