PIC16F872
9.2.18.17 BUS COLLISION DURING A STOP
CONDITION
The STOP condition begins with SDA asserted low.
When SDA is sampled low, the SCL pin is allow to float.
When the pin is sampled high (clock arbitration), the
baud rate generator is loaded with SSPADD<6:0> and
counts down to 0. After the BRG times out, SDA is
sampled. If SDA is sampled low, a bus collision has
occurred. This is due to another master attempting to
drive a data ’0’. If the SCL pin is sampled low before
SDA is allowed to float high, a bus collision occurs.
This is a case of another master attempting to drive a
data ’0’ (Figure 9-25).
Bus collision occurs during a STOP condition if:
a) After the SDA pin has been deasserted and
allowed to float high, SDA is sampled low after
the BRG has timed out.
b) After the SCL pin is deasserted, SCL is sampled
low before SDA goes high.
FIGURE 9-25: BUS COLLISION DURING A STOP CONDITION (CASE 1)
SDA sampled
low after TBRG,
Set BCLIF.
TBRG
TBRG
TBRG
SDA
SDA asserted low
SCL
PEN
BCLIF
P
’0’
’0’
’0’
’0’
SSPIF
FIGURE 9-26: BUS COLLISION DURING A STOP CONDITION (CASE 2)
TBRG
TBRG
TBRG
SDA
SCL goes low before SDA goes high
Set BCLIF
Assert SDA
SCL
PEN
BCLIF
P
’0’
’0’
SSPIF
DS30221A-page 82
Preliminary
1999 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
