PIC18F23K22 Datasheet, PDF (251/492 Pages) Microchip Technology – 28/40/44-Pin, Low-Power, High-Performance Microcontrollers with nanoWatt XLP Technology

PIC18(L)F2X/4XK22
15.6.13.2 Bus Collision During a Repeated
Start Condition
During a Repeated Start condition, a bus collision
occurs if:
a) A low level is sampled on SDAx when SCLx
goes from low level to high level.
b) SCLx goes low before SDAx is asserted low,
indicating that another master is attempting to
transmit a data ‘1’.
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.
If SDAx is low, a bus collision has occurred (i.e., another
master is attempting to transmit a data ‘0’, Figure 15-35).
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 Figure 15-36.
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.
FIGURE 15-36: BUS COLLISION DURING A REPEATED START CONDITION (CASE 1)
SDAx
SCLx
RSEN
Sample SDAx when SCLx goes high.
If SDAx = 0, set BCLxIF and release SDAx and SCLx.
BCLxIF
S
SSPxIF
Cleared by software
’0’
’0’
FIGURE 15-37:
BUS COLLISION DURING REPEATED START CONDITION (CASE 2)
TBRG
TBRG
SDAx
SCLx
BCLxIF
RSEN
S
SSPxIF
SCLx goes low before SDAx,
set BCLxIF. Release SDAx and SCLx.
Interrupt cleared
by software
’0’
 2010 Microchip Technology Inc.
Preliminary
DS41412B-page 251