Θεόδουλος Λιοντάκης

Δάσκαλος Πληροφορικής ΠΕ86

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I added the necessary signals to output the screen to a VGA monitor.

The signals that are generated are the R,G,B and H-SYNC, V-SYNCH.

In order to keep the Video memory needed down to 8K with current resolution of 300x208 the 8 supported colors can only be set per character line. So each line has a foreground and a background. It is fun trying to find ways  to do things with limited resources and with no help from custom chips but only with what you can design. You face the same problems of the home computer era.

 

Update 18/12/17 : video ram is now 16K, 384x248 pixels, 31x64 characters

Now each character haw its own background and foreground color of any of the 8 available.

 

Vga 8 colors

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I also added 32K of external RAM by adding 2 X UM61256FK-15 32Kx8bit static ram chips.

To do this test I added a Decod1 signal for address decoding that goes low when a valid address between 16384 and 49151 appears on the bus.

External ram test