The Serial Data (SDA) and Serial Clock (SCL) pins are used by the
I2C module to control the I2C bus lines. Unlike previous
versions of the MSSP, the SCL and SDA pins must be configured manually in open-drain
operation by setting the appropriate bits in the associated port’s Open-Drain Control
register (ODCON). Also unlike previous versions of the MSSP, the port’s Direction
Control register (TRIS) must have the SDA and SCL pins configured as outputs by clearing
the appropriate TRIS bits. Finally, slew rate control, internal pull-up resistor
selection, and input threshold levels for each pin can be configured using the RxyI2C
I2C Pad Control register.
Important: Note that previous
MSSP modules have recommended using external pull-up resistors rather than the internal
weak pull-ups. However, the internal pull-ups located on the dedicated I2C
pins may now be used, depending on the bus transmission frequency and capacitance. The
internal pull-ups can be configured in the RxyI2C register.
The SDA and SCL pins are typically assigned to two I/O port pins, and must be
enabled using the Peripheral Pin Select (PPS) module. The PPS module has two dedicated
I2C input registers: I2CxSCLPPS, which defines the SCL input pin, and
I2CxDATPPS, which defines the SDA input pin. SDA and SCL outputs are also defined via
the PPS module. The outputs use the RxyPPS registers to define the signal the pin will
output.
Important: Note that both the SDA
and SCL inputs and outputs must be defined, and must be assigned to the same pins. For
example, if the SDA pin is assigned to pin RC4, both the I2CxDATPPS and the RC4PPS
registers must be mapped to pin RC4. If both input and output signals are not mapped to
the same pin, or if one of the signals are not mapped at all, no communication will take
place.
The PPS module also allows for alternate pins to be used instead of the
default pin locations. If an alternate pin location is desired, simply load the
appropriate PPS registers with the new location.
Important: Note that some devices
allow digital peripherals to be relocated to any pin, while other devices only allow the
digital peripherals to be moved to pins within two I/O ports. Please refer to the device
data sheet’s PPS chapter for more details. Also, if the I2C pin locations are
moved from the default pins, the new locations may not be configured for I2C
levels, and would require the open-drain, slew rate, and input threshold control
registers to be configured for I2C levels, and the bus may require external
pull-up resistors since the weak pull-ups of non-I2C pins are not suitable
for communication.
