PIC18C242 MICROCHIP [Microchip Technology], PIC18C242 Datasheet - Page 148

• Manufacturer Part Number: PIC18C242
• Description: High-Performance Microcontrollers with 10-Bit A/D
• Manufacturer: MICROCHIP [Microchip Technology]

PIC18CXX2
14.3.16.2 BUS COLLISION DURING A REPEATED
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.
FIGURE 14-27: BUS COLLISION DURING A REPEATED START CONDITION (CASE 1)
FIGURE 14-28: BUS COLLISION DURING REPEATED START CONDITION (CASE 2)
DS39026B-page 148
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
START CONDITION
SCL goes low before SDA,
Set BCLIF. Release SDA and SCL
Preliminary
T
BRG
Sample SDA when SCL goes high.
If SDA = 0, set BCLIF and release SDA and SCL
If SDA is low, a bus collision has occurred (i.e. another
master, Figure 14-27, is attempting to transmit a data
’0’). If SDA is sampled high, the BRG is 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 condition,
Figure 14-28.
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 com-
plete.
T
Cleared in software
BRG
7/99 Microchip Technology Inc.
Interrupt cleared
in software
'0'
'0'
’0’