While the MPR121 IC already has several libraries for different platforms, other modules might not, so it becomes necessary to create them.This article was revised on 8 by Karl Söderby. This allows you to pass different values with ease and take advantage of object-oriented programming paradigms, such as inheritance and passing objects to other functions. Code portability is very important when writing programs for various systems, which is why it makes sense to create and use your own library. _BV(pin_to_read) //The _BV(n) macro simply means to left-shift a 1 n-spaces left (1 << n) /* Here it is in binaryĠ0000000000000100 //This equates to true Make a Custom LibraryĪfter getting to know which registers perform which operations, it gets a little tedious to write many instructions just to get a single value in several places. Now, to see if a pin is active, take that pin’s value and use it to shift a 1 that many spaces to the left, then do a bit-wise & operation to combine them. For example, imagine pins 2, 7, and 11 were active reg0 would be 10000100, and reg1 would be 00001000. Since reg1 is the MSB value, it needs to be bit-shifted 8 spaces to the left to allow for the LSB value, reg0, to be added on at the end. Uint16_t is the datatype for a number that is 2 bytes (hence the 16, which is the number of bits) and unsigned, which means it can only be positive, and it also means the first bit will not be treated as a sign flag. Then, combine them into a single unsigned int using: Read data from register 0x00 and 0x01, storing the 8-bit values into variables: To combine them into one larger value, the following operation is performed: This means that the data for the 12 pins is split between the two registers. The MPR121 stores pin states (0 or 1) in two bytes, with the LSB (Least Significant Bit) corresponding to either touch-pin 0 or touch-pin 8, since bytes have only 8 bits. For the MPR121, binary touch data is stored in registers 0x00 and 0x01.

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