16F876 Microchip Technology, 16F876 Datasheet - Page 91

• Manufacturer Part Number: 16F876
• Description: 28/40-pin 8-Bit CMOS FLASH Microcontrollers
• Manufacturer: Microchip Technology

9.2.18.2
During a Repeated Start condition, a bus collision
occurs if:
a)
b)
When the user deasserts 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 deasserted, 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’). If however SDA is
FIGURE 9-23: BUS COLLISION DURING A REPEATED START CONDITION (CASE 1)
FIGURE 9-24: BUS COLLISION DURING REPEATED START CONDITION (CASE 2)
1999 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
BUS COLLISION DURING A REPEATED
START CONDITION
’0’
’0’
’0’
’0’
SCL goes low before SDA,
Set BCLIF. Release SDA and SCL
T
BRG
Sample SDA when SCL goes high.
If SDA = 0, set BCLIF and release SDA and SCL
sampled high, the BRG is reloaded and begins count-
ing. 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, however, 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.
If at the end of the BRG time out both SCL and SDA are
still high, the SDA pin is driven low, the BRG is reloaded
and begins counting. At the end of the count, regard-
less of the status of the SCL pin, the SCL pin is driven
low and the Repeated Start condition is complete
(Figure
9-23).
T
Cleared in software
BRG
PIC16F87X
Interrupt cleared
in software
’0’
’0’
DS30292A-page 91
’0’
’0’