rp2040 Shift Register 74HC595 Library

C Library for working with the 74HC595 shift register.

Table of Content

• Example
• Documentation
  • PinConfig Object
  • ShiftRegister Object
  • API Functions
• Building the Examples
• Building the Tests
• License

Example

How to switch on 8 LEDs:

#include <rp2040_shift_register.h>

void main()
{
  ShiftRegister reg = shift_register_new((PinConfig){
      .SERIAL_PIN = 9,
      .SHIFT_REGISTER_CLOCK_PIN = 11,
      .STORAGE_REGISTER_CLOCK_PIN = 10});

  int switch_on = 0;

  while (true)
  {
    shift_register_write_bit(1, &reg);
    shift_register_flush(&reg);

    sleep_ms(1050);
    switch_on++;

    if (switch_on = 8)
    {
      shift_register_reset_storage(&reg);
      sleep_ms(1050);
      switch_on = 0;
    }
  }
}

Documentation

PinConfig Object

Define the three pins necessary for connecting Pico with the shift register chip.

• PinConfig.SERIAL_PIN
• PinConfig.SHIFT_REGISTER_CLOCK_PIN
• PinConfig.STORAGE_REGISTER_CLOCK_PIN

ShiftRegister Object

Object representing the shift register chip.

It has the following properties:

• ShiftRegister.SERIAL_PIN
• ShiftRegister.SHIFT_REGISTER_CLOCK_PIN
• ShiftRegister.LATCH_REGISTER_CLOCK_PIN
• ShiftRegister.serial_pin_state: The state of the SERIAL_PIN, which is 1 of 0
• ShiftRegister.register_state: The int8 value representing the current register

This object also defines its functions like write_bit, which you can call directly as &reg->write_bit(&reg, 1). However, it is encouraged to use the public functions defined below.

API Functions

• ShiftRegister shift_register_new(PinConfig): Create a new shift register object
• bool shift_register_write_bit(ShiftRegister *, bool): Write a single bit to the shift register, and perform a shift-right of all other bits. To output the shift registers' content, use shift_register_flush
• bool shift_register_write_bitmask(ShiftRegister *, u_int8_t): Write a complete bitmask, e.g. 0b10101010 to the register. To output the shift registers' content, use shift_register_flush
• bool shift_register_flush(ShiftRegister *): Flush the content of the shift register to the storage register.
• bool shift_register_reset(ShiftRegister *): Resets the shift register's content to bitmask 0b00000000.
• bool shift_register_reset_storage(ShiftRegister *) Resets the storage register's content to bitmask 0b00000000 and performs a shift_register_flush()
• char * shift_register_print(ShiftRegister \*) Prints the shift register's state as a bitmask, and returns a char* of the bitmask string.

Building the Examples

From the main directory:

rm -rvf build
cmake -B build -S . -DEXAMPLE_BUILD=ON
make -C build/example

Files are contained in `build/examples.

8_led_blink.bin
8_led_blink.dis
8_led_blink.elf
8_led_blink.elf.map
8_led_blink.hex
8_led_blink.uf2

Building the Tests

From the main directory, compile and run the tests.

rm -rvf build
cmake -B build -S . -DTEST_BUILD
make -C build/src && make -C build/test

Run tests with build/test/pico_shift_register.tests.bin

Runing Tests
[==========] Running 4 test(s).
[ RUN      ] test_shift_register_config
[       OK ] test_shift_register_config
[ RUN      ] test_write_bit
[0b01000000]
[       OK ] test_write_bit
[ RUN      ] test_write_bitmask
[0b00010000]
[       OK ] test_write_bitmask
[ RUN      ] test_reset_shift_register
[0b00000000]
[       OK ] test_reset_shift_register
[==========] 4 test(s) run.
[  PASSED  ] 4 test(s).

License

BSD-3-Clause