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Testing a VHDL LCD matrix display driver

Jan Cumps

image

I'm going to try out a VHDL driver for the Hitachi HD44780 LCD driver.
I've ported it for several microcontrollers (TI Hercules, Maxim MAX32660) and a Linux device in the past.
I was going to write a VHDL driver, but found a few potential candidates online. I'm going to try Daniel Kampert's HD44780 LCD-Interface.

Current status:

  • VHDL code analysed
  • Block diagram made:
    image

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  • Current status:

    • I used a raw LCD, not the SainSmart shield.
      The Arduino libraries do not use the R/W pin. On this shield, and compatibles, R/W is hard wired to ground.
      They just wait long enough before writing data, and always put the driver in write status.
      The VHDL library actually checks the driver register to see if it's ready for data.
      I could change the VHDL code, but I like the way they do this waiting on the driver ready signal.
    • I did change the VHDL code. For my own training I changed the interface from 8 bit to 4 bit.
      The 4 bit interface is a little slower, and a little more complex. But it's a good exercise to sharpen the skills

    image

Reply

  • Current status:

    • I used a raw LCD, not the SainSmart shield.
      The Arduino libraries do not use the R/W pin. On this shield, and compatibles, R/W is hard wired to ground.
      They just wait long enough before writing data, and always put the driver in write status.
      The VHDL library actually checks the driver register to see if it's ready for data.
      I could change the VHDL code, but I like the way they do this waiting on the driver ready signal.
    • I did change the VHDL code. For my own training I changed the interface from 8 bit to 4 bit.
      The 4 bit interface is a little slower, and a little more complex. But it's a good exercise to sharpen the skills

    image

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