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Help with 6845 CRTC needed

I am building a video circuit to use with a z80-based project.

I am looking to use a 6845 to give a screen resolution of 512*256 with

8 colours. I have a problem understanding the addressing of the 6845 - it seems to be only for use with character based video. I want to use one byte of screen memory to give me 2 pixels (I will have 2 bits left over for other uses - flashing etc). This means I have to address 64k memory and have 16 address lines. I also want that memory to be able to be accessed contiguously from 0 to 64k.

Can someone explain how this could be done?

Many thanks,

Matthew

Reply to
Matthew
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--------------- Why don't you just buy an old MGP or Hercules card? That's exactly what it is!

-Steve

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Reply to
R. Steve Walz

Because I want to make it myself.

Reply to
Matthew

"Matthew" schreef in bericht news: snipped-for-privacy@posting.google.com...

Matthew,

The 6845 *is* a character based CRT controller but a very versatile one. You can define the dimensions of a character and you can go graphical by defining a hight of one pixel.Can't remember whether the width also could by set to one pixel but the smaller the better. You need one address in the video memory (RAM) for every character on the screen. Translation to video is done during the scanning by a character generator, usually a bunch of (EP)ROM. No need to say you absolutely need a datasheet of the 6845.

petrus bitbyter

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Reply to
petrus bitbyter

there is one here :

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Jean-Yves.
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Jean-Yves

In message , Matthew writes

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Hope these are of use!

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Chris
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Chris

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