PIC16LF18854 Datasheet, PDF (471/668 Pages) Microchip Technology – C Compiler Optimized RISC Architecture

PIC16(L)F18856/76
31.4 I²C MODE OPERATION
All MSSP I²C communication is byte oriented and
shifted out MSb first. Six SFR registers and two
interrupt flags interface the module with the PIC^®
microcontroller and user software. Two pins, SDA and
SCL, are exercised by the module to communicate
with other external I²C devices.
31.4.1 BYTE FORMAT
All communication in I²C is done in 9-bit segments. A
byte is sent from a master to a slave or vice-versa, fol-
lowed by an Acknowledge bit sent back. After the
eighth falling edge of the SCL line, the device output-
ting data on the SDA changes that pin to an input and
reads in an acknowledge value on the next clock
pulse.
The clock signal, SCL, is provided by the master. Data
is valid to change while the SCL signal is low, and
sampled on the rising edge of the clock. Changes on
the SDA line while the SCL line is high define special
conditions on the bus, explained below.
31.4.2 DEFINITION OF I²C TERMINOLOGY
There is language and terminology in the description
of I²C communication that have definitions specific to
I²C. That word usage is defined below and may be
used in the rest of this document without explanation.
This table was adapted from the Philips I²C
specification.
31.4.3 SDA AND SCL PINS
Selection of any I²C mode with the SSPEN bit set,
forces the SCL and SDA pins to be open-drain. These
pins should be set by the user to inputs by setting the
appropriate TRIS bits.
Note 1: Data is tied to output zero when an I²C
mode is enabled.
2: Any device pin can be selected for SDA
and SCL functions with the PPS peripheral.
These functions are bidirectional. The SDA
input is selected with the SSPDATPPS
registers. The SCL input is selected with
the SSPCLKPPS registers. Outputs are
selected with the RxyPPS registers. It is the
user’s responsibility to make the selections
so that both the input and the output for
each function is on the same pin.
31.4.4 SDA HOLD TIME
The hold time of the SDA pin is selected by the SDAHT
bit of the SSPxCON3 register. Hold time is the time
SDA is held valid after the falling edge of SCL. Setting
the SDAHT bit selects a longer 300 ns minimum hold
time and may help on buses with large capacitance.
TABLE 31-1: I²C BUS TERMS
TERM
Description
Transmitter
The device which shifts data out
onto the bus.
Receiver
The device which shifts data in
from the bus.
Master
The device that initiates a transfer,
generates clock signals and termi-
nates a transfer.
Slave
The device addressed by the
master.
Multi-master
A bus with more than one device
that can initiate data transfers.
Arbitration
Procedure to ensure that only one
master at a time controls the bus.
Winning arbitration ensures that
the message is not corrupted.
Synchronization Procedure to synchronize the
clocks of two or more devices on
the bus.
Idle
No master is controlling the bus,
and both SDA and SCL lines are
high.
Active
Any time one or more master
devices are controlling the bus.
Addressed
Slave
Slave device that has received a
matching address and is actively
being clocked by a master.
Matching
Address
Address byte that is clocked into a
slave that matches the value
stored in SSPxADD.
Write Request
Slave receives a matching
address with R/W bit clear, and is
ready to clock in data.
Read Request
Master sends an address byte with
the R/W bit set, indicating that it
wishes to clock data out of the
Slave. This data is the next and all
following bytes until a Restart or
Stop.
Clock Stretching When a device on the bus hold
SCL low to stall communication.
Bus Collision
Any time the SDA line is sampled
low by the module while it is out-
putting and expected high state.
 2016 Microchip Technology Inc.
Preliminary
DS40001824A-page 471