Skip to content

peterw8102/vga-video

Folders and files

NameName
Last commit message
Last commit date

Latest commit

 

History

16 Commits
 
 
 
 
 
 
 
 

Repository files navigation

vga-video

8Bit VGA Video Card for my Z80 SBC. This repo will initially contain the code for the programmable logic devices and might eventually include some test/demo software for the card eventually.

This video adaptor is designed as a daughter card for my Z80 SBC and some understanding of the control signals on that card are useful.

Points to note:

  • The CPU board includes an I/O address decoder where spare lines are taken to the edge connector as the GIST_1-5 lines. This card uses GIST_5
  • The CPU board also includes a simple paged memory mapper mapping any 16KB from a 4MB address space into any of 4 16K slots in the native Z80 16 bit address space. The 8 extended address bits are taken to the expansion connector as BA21-BA14. This card uses these to decode the video memory to the top 16K page in the 4MB space.

GALS

The design uses a set of GAL programmable devices to provide most of the logic required to drive the card:

  • LINE_CNT - 10 bit counter that ticks out each bit in a horizontal scan line, resetting at a count of 800
  • LINE_DEC - Decodes values from LINE_CNT in conjunction with VERT_DEC signals to generate a set of control signals
  • VERT_CNT - 10 bit counter counting out each scan line from 0-524
  • VERT_DEC - Decodes the 10 bit VERT_CNT values to generate vertical control stignals
  • MEM_DEC - Very simple logic to interface the CPU to the dual port memory
  • IO_DEC - Completely unrelated to video, the card also includes an 8 bit input and an 8 bit input port, this decodes the control lines

About

8Bit VGA Video Card for my Z80 SBC

Resources

Stars

Watchers

Forks

Releases

No releases published

Packages

No packages published