PIC16F872 Datasheet, PDF (82/160 Pages) Microchip Technology – 28-Pin, 8-Bit CMOS FLASH Microcontroller

PIC16F872
9.2.18.17 BUS COLLISION DURING A STOP
CONDITION
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.
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).
FIGURE 9-25: BUS COLLISION DURING A STOP CONDITION (CASE 1)
TBRG
TBRG
TBRG
SDA
SDA sampled
low after TBRG,
Set BCLIF.
SDA asserted low
SCL
PEN
BCLIF
P _{’0’}
’0’
SSPIF
’0’
’0’
FIGURE 9-26: BUS COLLISION DURING A STOP CONDITION (CASE 2)
TBRG
TBRG
TBRG
SDA
SCL
Assert SDA
SCL goes low before SDA goes high
Set BCLIF
PEN
BCLIF
P
’0’
SSPIF ^{’0’}
DS30221A-page 82
Preliminary
© 1999 Microchip Technology Inc.