PIC16LF1503 Datasheet, PDF (206/340 Pages) Microchip Technology – 14-Pin Flash, 8-Bit Microcontrollers

PIC16(L)F1503
21.6.13.1 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 21-32).
b) SCLx is sampled low before SDAx is asserted
low (Figure 21-33).
During a Start condition, both the SDAx and the SCLx
pins are monitored.
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 21-32).
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.
If the SDAx pin is sampled low during this count, the
BRG is reset and the SDAx line is asserted early
(Figure 21-34). 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.
Note:
The reason that bus collision is not a fac-
tor 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
collision 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.
FIGURE 21-33:
SDAx
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.
SCLx
SEN
BCLxIF
S
Set SEN, enable Start
condition if SDAx = 1, SCLx = 1
SDAx sampled low before
Start condition. Set BCLxIF.
S bit and SSPxIF set because
SDAx = 0, SCLx = 1.
SEN cleared automatically because of bus collision.
SSPx module reset into Idle state.
SSPxIF and BCLxIF are
cleared by software
SSPxIF
SSPxIF and BCLxIF are
cleared by software
DS41607A-page 206
Preliminary
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