Microchip Technology MA160014 Data Sheet
PIC18(L)F2X/4XK22
DS41412F-page 256
2010-2012 Microchip Technology Inc.
15.6.13.3
Bus Collision During a Stop
Condition
Condition
Bus collision occurs during a Stop condition if:
a)
After the SDAx pin has been deasserted and
allowed to float high, SDAx is sampled low after
the BRG has timed out (Case 1).
allowed to float high, SDAx is sampled low after
the BRG has timed out (Case 1).
b)
After the SCLx pin is deasserted, SCLx is
sampled low before SDAx goes high (Case 2).
sampled low before SDAx goes high (Case 2).
The Stop condition begins with SDAx asserted low.
When SDAx is sampled low, the SCLx pin is allowed to
float. When the pin is sampled high (clock arbitration),
the Baud Rate Generator is loaded with SSPxADD and
counts down to zero. After the BRG times out, SDAx is
sampled. If SDAx is sampled low, a bus collision has
occurred. This is due to another master attempting to
drive a data ‘0’ (
When SDAx is sampled low, the SCLx pin is allowed to
float. When the pin is sampled high (clock arbitration),
the Baud Rate Generator is loaded with SSPxADD and
counts down to zero. After the BRG times out, SDAx is
sampled. If SDAx is sampled low, a bus collision has
occurred. This is due to another master attempting to
drive a data ‘0’ (
). If the SCLx pin is
sampled low before SDAx is allowed to float high, a bus
collision occurs. This is another case of another master
attempting to drive a data ‘0’ (
collision occurs. This is another case of another master
attempting to drive a data ‘0’ (
).
FIGURE 15-38:
BUS COLLISION DURING A STOP CONDITION (CASE 1)
FIGURE 15-39:
BUS COLLISION DURING A STOP CONDITION (CASE 2)
SDAx
SCLx
BCLxIF
PEN
P
SSPxIF
T
BRG
T
BRG
T
BRG
SDAx asserted low
SDAx sampled
low after T
low after T
BRG
,
set BCLxIF
’0’
’0’
SDAx
SCLx
BCLxIF
PEN
P
SSPxIF
T
BRG
T
BRG
T
BRG
Assert SDAx
SCLx goes low before SDAx goes high,
set BCLxIF
set BCLxIF
’0’
’0’