PIC16(L)F1508/9
DS40001609E-page 184
2011-2015 Microchip Technology Inc.
21.4.5
START CONDITION
The I
2
C specification defines a Start condition as a
transition of SDAx from a high to a low state while
SCLx line is high. A Start condition is always gener-
ated by the master and signifies the transition of the
bus from an Idle to an Active state.
shows wave forms for Start and Stop conditions.
A bus collision can occur on a Start condition if the
module samples the SDAx line low before asserting it
low. This does not conform to the I
2
C Specification that
states no bus collision can occur on a Start.
21.4.6
STOP CONDITION
A Stop condition is a transition of the SDAx line from
low-to-high state while the SCLx line is high.
21.4.7
RESTART CONDITION
A Restart is valid any time that a Stop would be valid.
A master can issue a Restart if it wishes to hold the
bus after terminating the current transfer. A Restart
has the same effect on the slave that a Start would,
resetting all slave logic and preparing it to clock in an
address. The master may want to address the same or
another slave.
Restart condition.
In 10-bit Addressing Slave mode a Restart is required
for the master to clock data out of the addressed
slave. Once a slave has been fully addressed, match-
ing both high and low address bytes, the master can
issue a Restart and the high address byte with the
R/W bit set. The slave logic will then hold the clock
and prepare to clock out data.
After a full match with R/W clear in 10-bit mode, a prior
match flag is set and maintained. Until a Stop condi-
tion, a high address with R/W clear, or high address
match fails.
21.4.8
START/STOP CONDITION INTERRUPT
MASKING
The SCIE and PCIE bits of the SSPxCON3 register
can enable the generation of an interrupt in Slave
modes that do not typically support this function. Slave
modes where interrupt on Start and Stop detect are
already enabled, these bits will have no effect.
FIGURE 21-12:
I
2
C START AND STOP CONDITIONS
FIGURE 21-13:
I
2
C RESTART CONDITION
Note:
At least one SCLx low time must appear
before a Stop is valid, therefore, if the SDAx
line goes low then high again while the SCLx
line stays high, only the Start condition is
detected.
SDAx
SCLx
P
Stop
Condition
S
Start
Condition
Change of
Data Allowed
Change of
Data Allowed
Restart
Condition
Sr
Change of
Data Allowed
Change of
Data Allowed
