| Re: Z80 MC6845 video board examples [message #9930 is a reply to message #9881] |
Tue, 17 May 2022 06:09  |
etchedpixels
Messages: 333
Registered: October 2015
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Senior Member |
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There's also the keep writing the last thing on the dead cycle approach where your video memory is write only.
CPU address and data to the video RAM are latched when they happen and the video side runs with the 6845 access half of the cycle reading, then the other half of the cycle sets write on the ram for most of the cycle, so that the last byte buffered keeps getting written into the RAM when the video memory is free. Write only but no wait states and the CPU is usually unable to write to video fast enough to need nops between updates. And of course you can shadow it with RAM if you need to.
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