Controlling HD44780 display with Raspberry Pi Pico
This is my first attempt to program RaspberryPi PIO and DMA. I wanted to control HD44780 display with simple API and without bit banging.
Program uses small fifo which contains data to send to display. You can control size of the fifo by changing value of HD44780_BUFFERSIZE. If there is free space in fifo, functions for sending data to display do not block and data are send to display in background by DMA/PIO.
Many programmers use only write mode (RW pin is connected to GND). They have to count with the time display need to process data. I use different method where BUSY flag is read from display back (RW pin is controlled).
PIN N+0 = D4
PIN N+1 = D5
PIN N+2 = D6
PIN N+3 = D7
PIN N+4 = RS
PIN N+5 = RW
PIN N+6 = E
Value of N is set in hd44780_init function.
My display can be powered by 3.3V so if RW pin is HI there is correct voltage on input pins of pico. If you use different voltage, some extra circuit must be used. In my example I use pins 16 to 22.
Use function hd44780_init to initialize library. You can pass pio and sm arguments to select which PIO and state machine is used. Pin N is defined by argument pin last argument defines frequency.
After that you can use functions hd44780_* to control display - they are described in datasheet of HD44780.
When 2MHz frequency is used, I managed to draw approx. 300frames per second.
This is only attempt to learn something new. This is definitely not the best implementation. If you know better way, how to do it, let me know :)