FYI: storing demos in battery-backed RAM

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Glenn Roberts

Sep 21, 2021, 4:38:56 PMSep 21

Recall that I’m planning to demo three H8 configurations at VCF: “classic” system ca. 1978, “gaming” system ca. 1980/81 and “modern” system (H8-2020).


For the “classic” system I want to be able to keep some demos in battery-backed ram so that I can just cue up the Program Counter, hit “GO” and run.  This capability is enabled by Norberto’s “H8 8080A/Z80 64K RAM ORG0 BOARD”


(OK so I’m cheating a little in using a “modern” RAM board in a “classic” configuration, but I want reliability and flexibility so I sacrificed realism for the cause. But to be fair I’ve got the board set for only 24K of RAM starting at 040.000!)


One nice feature is that that the board has 128K of physical RAM – you can toggle the 17th address bit to switch to the “hidden” RAM.  This allows me to load up some standard demos in the extended RAM and flip to it any time I just want to display eye candy.  Then to go back and boot the system or load from tape I switch to the other RAM bank. Since they’re battery backed up there’s essentially zero boot time.  Great feature!  For now I just installed a simple “L” bracket to hold a small toggle switch:


(the ribbon cables in that picture go to a large LED slave display that I hope will be a visual draw to the exhibit):



  • Glenn


Norberto Collado

Sep 22, 2021, 12:43:40 AMSep 22

That is going to be a great H8 VCF show. Take a lot of pictures.


I wonder for next year at VCF what we can do to bring the H8 demo another notch up? A bigger WOW! It will be nice to plan ahead to ring out any HW issues.


Thanks for keeping the H8 alive!



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Norberto Collado

Sep 22, 2021, 1:41:00 AMSep 22

For Q2’22 I hope to have the following boards working:


  1. Z80 CPU with 1MB of RAM on same board. I need to use more GALS to make more space on current Z80 V4 board. Same functionality as the Z80 V4 board. This should be last Z80 CPU board and shall run at 20MHz and also we will gain another H8 slot as the 512KB RAM board will not be needed.
  2. Network with Dual SDC support and bootable. Can access files over the internet. Will love to see HDOS booting from the SDC cards.
  3. DUAL GIDE. Can boot from four CF cards. Will love to see HDOS booting from the CF cards.   
  4. Z67-SDC+ - Replacement for Z67-IDE+. Same size using easy to find parts.
  5. + other boards that Terry S. is working on.


I hope to start working on winter Q4’22 on my H17 floppy RAW SSD drive project. It just works as a regular floppy H17 floppy to interface to the H17 controller. This shall be the Z67-SDC+ companion. It has been in my To-Do-List since I started the Z67-IDE+ as my real H17 floppies are dying slowly. Two weeks ago I lost another 5.25” floppy drive and I’m down to 1 that I bought in eBay; new unused. The GOTEK is not that reliable, the SVD needs a laptop to be functional, etc. I have all the parts in a box to put it together and I just need to work on the FW when I get time. It is based on a Z80 with a lot of high speed RAM and a single CF card for storage. Also, it will allow me to learn on the floppy drive insights.


Z80 with 1MB preview: WIP and layout needs to be clean up.


Note: It will be Rev 5.0 and I ram out of space, so need to use GALS to gain more board space to finalized routing.






Glenn Roberts

Sep 22, 2021, 10:56:00 AMSep 22

Wow. The hits just keep on comin…


I’m sure we can get HDOS to boot from any of these new devices. happy to help once I can get my hands on the hardware…

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