Newhaven Products > Character LCDs

NHD-0420H1Z-FL-GBW-33V3 pull-ups and pull-downs in 4 bit mode


Can anyone confirm the NHD-0420H1Z-FL-GBW-33V3 does or does not require pull-ups on E,RS,andR/W?  Additionally, in 4-bit mode are there internal pull-downs on the low nibble lines.  Is the external circuit expected to provide either pull-ups or pull-downs in 4-bit mode on any lines?

No pull-ups/pull-downs are required on any of the signals on this display (even in 4-bit mode).  You may view in the datasheet that the wiring diagram for the display shows only one resistor, and it is adjustable (potentiometer) to allow for contrast adjustment.

Great, thank you.  I did see the diagram in the data sheet, in addition to the internal wiring diagram in the ST7066U manual showing pull-ups on RS and R/W but not E - both great references.  It seemed clear but I wanted to get a confirmation just in case.

We are stuck on the use of the NHD-0420H1Z-FL-GBW-33V3.  The display does illuminate when powered and initialized but no cursor or characters are ever visible.  It also seems as if the DDRAM addresses are not incrementing when data is written to them or event when an explicit address command is sent to the controller.  Oddly, the BF does seem to be working...

I was hoping there was a requirement for external components and that perhaps floating lines were responsible - on the off chance they would stop the controller from initializing properly if they were absent.

Given that is not the case - can you suggest a means to troubleshoot the internal state of the controller?  How can we verify it is in fact initialized?  Is there, for example, a DDRAM location I can attempt to read that holds the current Function Set data?  I could write various values via Function Set and read them back to verify their application.

Another thought is that perhaps the voltages to VDD, V0, and LED+ are misconfigured - high V0 for example (V0 = VDD).  But if that were the case I would expect the call to set the AC or calls to write characters would result in those address values coming back with the BF.

The BF would be the only way I know of to check the internal state of the controller.  What voltage are you applying to V0?  The reason I ask is because it may be possible you have characters on the screen but cannot see them due to improper contrast voltage.  Do you have any character LCD library functions you are using, or is your code from scratch?  Have you successfully used this setup to communicate to an LCD previously?


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