I got one of these for very cheap though never got it going: https://datasheetspdf.com/pdf-file/5363 ... /EW32F50/1

The one I have requires -27v for contrast. How are you planning on generating the negative voltage? I see 8BIT is using an AA9090A running off 12v. Someone got one of the LCDs going using three 9v batteries, though I was hoping to generate it from the same 5v power source as everything else.

One thing, at least for the model I have, is that you need to start up the LCD first then apply the negative voltage after it's started. Not sure if that's something useful to try for yours.

I'm using a separate adjustable bench power supply to provide the negative voltage right now. Once I got it working, I will need to figure out how to generate -16V from 5V, don't think a simple charge pump doubler will do, need a bona fide booster converter.
Bill

The Z-80 has DMA capability which would increase efficiency for refreshing the display. I would not give up on that idea. I did do a composite video graphical display with an ATMega1284 which included the AVR doing Line, Box, and circle generation along with text. I cannot speak to the speed at this point as I don't recall, but it did work. It also had the option to output to an LCD.

Daryl

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In the Z80 world I probably would use a Z280 which has 4 DMA channels built in. Since this is 6502 forum, I thought I'd try it again using my newly developed 6502 SBC with the help of a CPLD I/O board. The CPLD I/O board was a CF drive interface board re-purposed as LCD interface. I'll need to make some cuts and jumpers and reprogram the CPLD, but conceptually it looks like the attached photos.

Daryl,
Sometimes just KNOWING that I'm on the right track is enough to solve the problem. Before I dive into your ATmega program trying to understand yet another assembly language, I thought I take another fresh look at my LCD interface logic and software since I'm using a new CPLD board with 6502. I found a couple mistakes and fixed them. Now I can actually display a pattern on the LCD! This is very encouraging.

I'm glad you are making headway! If it helps, the only file you need to focus on is "vidgen.asm" It does all of the refresh based on an interrupt.

In Vid-LCD.asm, I set up a timer interrupt to provide 1 interrupt every 55.6us (microseconds). This does a refresh of 1 line. Doing the math, it completes a frame every 13.3mS, which is a 74.9Hz frame rate.

I don't recall the time needed to generate 1 line, but counting cycles in the code would provide that data.

Hope that helps.

Daryl

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This is the program driving the display in my previous post. The display memory is 10K from 0xC000-0xE7FF. It started off with random display data and then filled it with one-byte pattern every frame. It took 2 minutes 10 seconds to fill the entire display this way. So that's 10K frames in 130 seconds or 74 frames per second, which is what I measured with a scope. This is 6502 is running flat out moving display data to the LCD display, not very good use of a 6502, but now I understand how it works, I can start to replace the software with hardware.