PIC16F/LF1946/47
If the SDAx pin is sampled low during this count, the
BRG is reset and the SDAx line is asserted early
(Figure 23-34). If, however, a ‘1’ is sampled on the
SDAx pin, the SDAx pin is asserted low at the end of
the BRG count. The Baud Rate Generator is then
reloaded and counts down to zero; if the SCLx pin is
sampled as ‘0’ during this time, a bus collision does not
occur. At the end of the BRG count, the SCLx pin is
asserted low.
23.6.13.1 Bus Collision During a Start
Condition
During a Start condition, a bus collision occurs if:
a) SDAx or SCLx are sampled low at the beginning
of the Start condition (Figure 23-32).
b) SCLx is sampled low before SDAx is asserted
low (Figure 23-33).
During a Start condition, both the SDAx and the SCLx
pins are monitored.
Note:
The reason that bus collision is not a factor
during a Start condition is that no two bus
masters can assert a Start condition at the
exact same time. Therefore, one master
will always assert SDAx before the other.
This condition does not cause a bus colli-
sion because the two masters must be
allowed to arbitrate the first address fol-
lowing the Start condition. If the address is
the same, arbitration must be allowed to
continue into the data portion, Repeated
Start or Stop conditions.
If the SDAx pin is already low, or the SCLx pin is
already low, then all of the following occur:
• the Start condition is aborted,
• the BCLxIF flag is set and
•
the MSSPx module is reset to its Idle state
(Figure 23-32).
The Start condition begins with the SDAx and SCLx
pins deasserted. When the SDAx pin is sampled high,
the Baud Rate Generator is loaded and counts down. If
the SCLx pin is sampled low while SDAx is high, a bus
collision occurs because it is assumed that another
master is attempting to drive a data ‘1’ during the Start
condition.
FIGURE 23-33:
BUS COLLISION DURING START CONDITION (SDAX ONLY)
SDAx goes low before the SEN bit is set.
Set BCLxIF,
S bit and SSPxIF set because
SDAx = 0, SCLx = 1.
SDAx
SCLx
SEN
Set SEN, enable Start
condition if SDAx = 1, SCLx = 1
SEN cleared automatically because of bus collision.
SSPx module reset into Idle state.
SDAx sampled low before
Start condition. Set BCLxIF.
S bit and SSPxIF set because
SDAx = 0, SCLx = 1.
BCLxIF
SSPxIF and BCLxIF are
cleared by software
S
SSPxIF
SSPxIF and BCLxIF are
cleared by software
2010 Microchip Technology Inc.
Preliminary
DS41414A-page 277
MICROCHIP [ MICROCHIP ]
