Datasheet

PICkit™ 3 Debug Express Lessons

3.4 LESSON 4: SWITCH INPUT

The demo board switch is used in the lesson to rotate the LEDs once on each press.

3.4.1 Files and the #define Directive

This lesson has added a header file to the project named

04 Switch Input.h

as shown in Figure 3-20.

FIGURE 3-20: HEADER FILE

While it is assumed that the reader is familiar with C language header files, we’ll note

that in the 04 Switch Input.h header file the #define directive has been used to

give more meaningful names to the switch I/O pin variable and a constant value.

As with other C compilers use of #define, MPLAB C will replace all instances of the

text “Switch_Pin” with the text “PORTBbits.RB0” at compile time. Remember, for the

compiler to know about the #define definitions, the header file must be included in

the C file, as is done in 04 Switch Input.c:

#include "04 Switch Input.h" // header file

Key Concepts

- The directive #define can be used to give SFR registers and bits more

meaningful names.

- I/O pins that share an analog input channel must be configured as digital

pins if used as digital inputs using SFR ADCON1, or they will always read

‘0’.

- The PORTx SFRs are used to read the logic state on an input port pin.

- Mechanical switch debouncing can be handled in software to eliminate

external components that may be otherwise required.

#define Switch_Pin PORTBbits.RB0

#define DetectsInARow 5