11.4.9.2 Pin Control Summary

When a peripheral is enabled, the associated pin output drivers are typically module controlled, while a few are user-settable. The term, “module control”, means that the associated port pin output driver is disabled, and the pin can only be controlled and accessed by the peripheral. The term, “user settable”, means that the associated peripheral port pin output driver is user-configurable in software through the associated TRISx Special Function Register (SFR). The TRISx register must be set for the peripheral to function properly. For “user-settable” peripheral pins, the actual port pin state can always be read through the PORTx SFR.

An input capture peripheral provides an example of a user-settable peripheral. The user application must write the associated TRISx register to configure the input capture pin as an input. Because the I/O pin circuitry is still active when the input capture is enabled, the following method can be used to manually produce capture events using software:

• The input capture pin is configured as an output using the associated TRISx register.
• Then, the software can write values to the corresponding LATx register drive to internally control the input capture pin and force capture events.

As another example, an INTx pin can be configured as an output, and then by writing to the associated LATx bit, an INTx interrupt, if enabled, can be generated.

The UART is an example of a module control peripheral. When the UART is enabled, the PORTx and TRISx registers have no effect and cannot be used to read or write the RX and TX pins. Most communication peripheral functions available on the devices are module control peripherals.

For example, the SPI module can be configured for Host mode, in which only the SDO pin is required. In this scenario, the SDI pin can be configured as a general purpose output pin by clearing (setting to a logic ‘0’) the associated TRISx bit. For more information on how pins can be configured for a module, refer to the specific module section.