PIC18C658 MICROCHIP [Microchip Technology], PIC18C658 Datasheet - Page 165

• Manufacturer Part Number: PIC18C658
• Description: High-Performance Microcontrollers with CAN Module
• Manufacturer: MICROCHIP [Microchip Technology]

15.4.16.2 Bus Collision During a Repeated START
During a Repeated START condition, a bus collision
occurs if:
a)
b)
When the user de-asserts SDA and the pin is allowed
to float high, the BRG is loaded with SSPADD<6:0>
and counts down to 0. The SCL pin is then de-asserted,
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’, see
Figure 15-24). If SDA is sampled high, the BRG is
FIGURE 15-24: BUS COLLISION DURING A REPEATED START CONDITION (CASE 1)
FIGURE 15-25: BUS COLLISION DURING REPEATED START CONDITION (CASE 2)
 2000 Microchip Technology Inc.
A low level is sampled on SDA when SCL goes
from low level to high level.
SCL goes low before SDA is asserted low, indi-
cating that another master is attempting to trans-
mit a data ’1’.
SDA
SCL
BCLIF
RSEN
S
SSPIF
SDA
SCL
RSEN
BCLIF
S
SSPIF
Condition
SCL goes low before SDA.
Set BCLIF, release SDA and SCL.
Advanced Information
T
BRG
Sample SDA when SCL goes high.
If SDA = 0, set BCLIF and release SDA and SCL.
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 condi-
tion (Figure 15-25).
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.
T
Cleared in software.
BRG
PIC18CXX8
Interrupt cleared
in software.
'0'
'0'
DS30475A-page 165
’0’