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Re: Convert 16x2 chars display to big TFT display

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On 9/21/2021 3:31 AM, pozz wrote:
> I have a CPU board that interfaces to a standard 16x2 chars display, based on 
> HD44780 controller.
> 
> I'd like to replace this display with a full-color big TFT display, maybe 10", 
> but I can't change the firmware of the CPU (because I don't have the source 
> code and I can't rewrite it, because of cost and time).
> 
> The simple idea is to create an interface between the current CPU board and the 
> TFT display. This interface should be able to detect the signals from the CPU 
> and that was directed to HD44780, interpret the instructions (write CGRAM/DDRAM 
> and so on) and write the same things to the big TFT display.
> 
> Of course, exactly the same texts will be written on TFT display (of course 
> with a bigger and visible font) and this is acceptable.
> 
> So the MCU on the interface should be able to read 8 data bits, RS and R/W 
> signals syncronous to signal E.
> 
> I'm thinking to configure E signal as an external interrupt on the falling 
> edge. In the interrupt, I read data bits, R/W and RS and decode the instruction 
> or data.
> 
> Any suggestions? Maybe a similar code is already online.

You will likely find there are issues that you've not even considered
that the original software relies on (directly or indirectly).

Can your emulation handle a *steady* stream of reads/writes?  Or,
are you expecting the host to be gentle with the display interface?
Keep in mind, that you have to run a fair bit of code to paint
pels onto the display from "character codes".

Does the host rely on the timing of the display's "busy" indication
in any way?  Are there any bug in the display controller that
the host code works around -- that you'd have to emulate (but
aren't disclosed in the datasheet because they *are* bugs)?
Are the visual characteristics of your display similar to those
of the original display?  Cursor/character blink and other
attributes?

Put a pair of back-to-back latches on the data bus and some
steering logic and don't sweat the fine-grained timing issues.

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Thread

Convert 16x2 chars display to big TFT display pozz <pozzugno@gmail.com> - 2021-09-21 12:31 +0200
  Re: Convert 16x2 chars display to big TFT display Reinhardt Behm <rbehm@hushmail.com> - 2021-09-21 13:44 +0000
    Re: Convert 16x2 chars display to big TFT display pozz <pozzugno@gmail.com> - 2021-09-21 16:01 +0200
      Re: Convert 16x2 chars display to big TFT display Reinhardt Behm <rbehm@hushmail.com> - 2021-09-21 15:07 +0000
      Re: Convert 16x2 chars display to big TFT display Stef <me@this.is.invalid> - 2021-09-21 17:09 +0200
        Re: Convert 16x2 chars display to big TFT display pozz <pozzugno@gmail.com> - 2021-09-21 18:48 +0200
  Re: Convert 16x2 chars display to big TFT display Don Y <blockedofcourse@foo.invalid> - 2021-09-21 19:34 -0700
    Re: Convert 16x2 chars display to big TFT display olaf <olaf@criseis.ruhr.de> - 2021-09-22 06:04 +0200
      Re: Convert 16x2 chars display to big TFT display Don Y <blockedofcourse@foo.invalid> - 2021-09-21 21:38 -0700
    Re: Convert 16x2 chars display to big TFT display pozz <pozzugno@gmail.com> - 2021-09-22 08:49 +0200
      Re: Convert 16x2 chars display to big TFT display Don Y <blockedofcourse@foo.invalid> - 2021-09-22 00:58 -0700
      Re: Convert 16x2 chars display to big TFT display Rick C <gnuarm.deletethisbit@gmail.com> - 2021-10-01 21:52 -0700
    Re: Convert 16x2 chars display to big TFT display Rick C <gnuarm.deletethisbit@gmail.com> - 2021-10-01 21:40 -0700
  Re: Convert 16x2 chars display to big TFT display Michael Schwingen <news-1513678000@discworld.dascon.de> - 2021-10-31 14:42 +0000

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