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2012 Microchip Technology Inc.
Preliminary
DS41624B-page 217
PIC16(L)F1512/3
20.6.5
I2C MASTER MODE REPEATED
START CONDITION TIMING
A Repeated Start condition occurs when the RSEN bit
of the SSPCON2 register is programmed high and the
Master state machine is no longer active. When the
RSEN bit is set, the SCL pin is asserted low. When the
SCL pin is sampled low, the Baud Rate Generator is
loaded and begins counting. The SDA pin is released
(brought high) for one Baud Rate Generator count
(TBRG). When the Baud Rate Generator times out, if
SDA is sampled high, the SCL pin will be deasserted
(brought high). When SCL is sampled high, the Baud
Rate Generator is reloaded and begins counting. SDA
and SCL must be sampled high for one TBRG. This
action is then followed by assertion of the SDA pin
(SDA = 0) for one TBRG while SCL is high. SCL is
asserted low. Following this, the RSEN bit of the
SSPCON2 register will be automatically cleared and
the Baud Rate Generator will not be reloaded, leaving
the SDA pin held low. As soon as a Start condition is
detected on the SDA and SCL pins, the S bit of the
SSPSTAT register will be set. The SSPIF bit will not be
set until the Baud Rate Generator has timed out.
FIGURE 20-27:
REPEAT START CONDITION WAVEFORM
20.6.6
I2C MASTER MODE
TRANSMISSION
Transmission of a data byte, a 7-bit address or the
other half of a 10-bit address is accomplished by simply
writing a value to the SSPBUF register. This action will
set the Buffer Full flag bit, BF and allow the Baud Rate
Generator to begin counting and start the next trans-
mission. Each bit of address/data will be shifted out
onto the SDA pin after the falling edge of SCL is
asserted. SCL is held low for one Baud Rate Generator
rollover count (TBRG). Data should be valid before SCL
is released high. When the SCL pin is released high, it
is held that way for TBRG. The data on the SDA pin
must remain stable for that duration and some hold
time after the next falling edge of SCL. After the eighth
bit is shifted out (the falling edge of the eighth clock),
the BF flag is cleared and the master releases SDA.
This allows the slave device being addressed to
respond with an ACK bit during the ninth bit time if an
address match occurred, or if data was received prop-
erly. The status of ACK is written into the ACKSTAT bit
on the rising edge of the ninth clock. If the master
receives an Acknowledge, the Acknowledge Status bit,
ACKSTAT, is cleared. If not, the bit is set. After the ninth
clock, the SSPIF bit is set and the master clock (Baud
Rate Generator) is suspended until the next data byte
is loaded into the SSPBUF, leaving SCL low and SDA
After the write to the SSPBUF, each bit of the address
will be shifted out on the falling edge of SCL until all
seven address bits and the R/W bit are completed. On
the falling edge of the eighth clock, the master will
release the SDA pin, allowing the slave to respond with
an Acknowledge. On the falling edge of the ninth clock,
the master will sample the SDA pin to see if the address
was recognized by a slave. The status of the ACK bit is
loaded into the ACKSTAT Status bit of the SSPCON2
register. Following the falling edge of the ninth clock
transmission of the address, the SSPIF is set, the BF
flag is cleared and the Baud Rate Generator is turned
off until another write to the SSPBUF takes place,
holding SCL low and allowing SDA to float.
Note 1:
If RSEN is programmed while any other
event is in progress, it will not take effect.
2:
A bus collision during the Repeated Start
condition occurs if:
SDA is sampled low when SCL
goes from low-to-high.
SCL goes low before SDA is
asserted low. This may indicate
that another master is attempting to
transmit a data ‘1’.
SDA
SCL
Repeated Start
Write to SSPCON2
Write to SSPBUF occurs here
At completion of Start bit,
hardware clears RSEN bit
1st bit
S bit set by hardware
TBRG
SDA = 1,
SCL (no change)
SCL = 1
occurs here
TBRG
and sets SSPIF
Sr