The SP0770 keypad is a device that provides additional functionality by introducing a compact matrix of buttons. Each button can be used to perform a unique task, such as changing the channel on a television.
/* Keypad: 3 x 4 (library) */
/* Filename: Keypad.h */
/* Author: Michael */
void Keypad(void)
{
Keypad_R1 = 1; // Set Keypad Row #1 HIGH
Keypad_R2 = 0; // Set Keypad Row #2 LOW
Keypad_R3 = 0;
Keypad_R4 = 0;
if (Keypad_C1 == 1) // If Keypad Column #1 reads HIGH
{
// Do something
while (Keypad_C1 == 1); // Wait for Keypad [1] to be released
}
else if (Keypad_C2 == 1) // If Keypad Column #2 reads HIGH
{
// Do something
while (Keypad_C2 == 1); // Wait for Keypad [2] to be released
}
else if (Keypad_C3 == 1) // If Keypad Column #3 reads HIGH
{
// Do something
while (Keypad_C3 == 1); // Wait for Keypad [3] to be released
}
else
{
Keypad_R1 = 0;
Keypad_R2 = 1;
Keypad_R3 = 0;
Keypad_R4 = 0;
if (Keypad_C1 == 1)
{
// Do something
while (Keypad_C1 == 1); // Wait for Keypad [4] to be released
}
else if (Keypad_C2 == 1)
{
// Do something
while (Keypad_C2 == 1); // Wait for Keypad [5] to be released
}
else if (Keypad_C3 == 1)
{
// Do something
while (Keypad_C3 == 1); // Wait for Keypad [6] to be released
}
else
{
Keypad_R1 = 0;
Keypad_R2 = 0;
Keypad_R3 = 1;
Keypad_R4 = 0;
if (Keypad_C1 == 1)
{
// Do something
while (Keypad_C1 == 1); // Wait for Keypad [7] to be released
}
else if (Keypad_C2 == 1)
{
// Do something
while (Keypad_C2 == 1); // Wait for Keypad [8] to be released
}
else if (Keypad_C3 == 1)
{
// Do something
while (Keypad_C3 == 1); // Wait for Keypad [9] to be released
}
else
{
Keypad_R1 = 0;
Keypad_R2 = 0;
Keypad_R3 = 0;
Keypad_R4 = 1;
__delay_ms(100);
if (Keypad_C1 == 1)
{
// Do something
while (Keypad_C1 == 1); // Wait for Keypad [*] to be released
}
if (Keypad_C2 == 1)
{
// Do something
while (Keypad_C2 == 1); // Wait for Keypad [0] to be released
}
else if (Keypad_C3 == 1)
{
// Do something
while (Keypad_C3 == 1); // Wait for Keypad [#] to be released
}
}
}
}
}The SP0770 is a 3×4 (3 columns and 4 rows) keypad, as shown in Figure 1, there are seven terminals, each of which connects to either a column or row.
Columns C1 to C2 can be connected to three pins, configured as read/input (PORT), on an MCU. Rows R1 to R4 can be connected to four pins, configured as write/output (LAT), on an MCU. Pressing Key #1 connects C1 to R1, resulting in the MCU pin, connected to C1, reading HIGH. This is assuming the MCU pin, connected to R1, is at a HIGH state. The MCU pins connected to each of the four rows can be individually set to HIGH in sequence to distinguish which button is pressed. The keypad_R1 word, as shown in the code at line #8, can be defined in the source code as an association with a particular MCU pin and function; for example, #define Keypad_R1 LATBbits.LATB14. The same approach can be applied to all other MCU pins used for the keypad. The following code instructs the MCU to send a HIGH signal on one of the four rows, after which each column is read for a HIGH signal. The “Do something” comment marks the place at which code can be executed to achieve a particular result.