Joe: this is the same board I have in Rusty and I actually have a second one of these – both in operational condition. The Rev 2.6 board is the last iterative improvement that Norberto made of the original “Les Bird” Z80 board. Subsequently Norberto incorporated the speed function and other capabilities directly on the CPU board (Revs 3.1 and up).
This configuration has run rock steady for me for a long time.
I took pictures of my second Rev 2.6 board, which is configured for stand alone operation. The system has only the CPU board and the Speed board installed. Pix here:
CPU board: https://photos.app.goo.gl/VHhp7X131ZPuFkCt7
Speed board: https://photos.app.goo.gl/hUnBy8VJw29ePre96
I realize you’re trying to test the CPU board initially (without the speed board). I would recommend using header pins and shorting blocks on the “A B” configuration area for CPU speed. I’m not sure how to configure those pins. on my system nothing is connected there as the speed board does the work. Les had some documentation on how to set these in his original writeup: https://sebhc.github.io/sebhc/pcbs/H8-Z80-64_Rev2.pdf. Again, when using the speed board I have no jumpers set there so I recommend headers/shorting blocks for configuring this part of the board.
One thing I notice is you don’t have a jumper on the 555 circuit. You have to pick whether you want the LM555 of Front Panel to do the reset function. I have mine set for “LM” (LM555).
On mine I do not have a jumper on the “X” jumper.
You also seem to have the jumper (bottom right) set for “H37” – that’ll definitely cause a problem. move that to the left two pins.
Try those changes and see what happens…
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Joe: according to David Troendle’s writeup on the Z80 Rev2 board the A B jumpers you have are installed correctly for use with a 2 Mhz oscillator:
but you probably already knew that… 😊
I do believe you’ll have to remove those jumpers when you go to use the speed board…
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Norberto, do you know if this CPU board worked before I got it from you?
Yes, it was functional before. I used it a lot.
Please send me the CPU board back to check it out. Also, I ordered some 8080A/Z80 RAM boards as I have several users asking for such board. Because of all the pain the Z80 is causing you, I will give you a RAM pcb board that can run at 10MHZ. You can put in any slot in the H8 chassis once assembled. Also, I will include the 8080A EEPROM adapter as well as I need you to verify its operation using the 8080A CPU board.
Joe: a few more tips to possibly help get your board working:
I have installed these two boards in an H8 chassis and they operate fine. I suggest you exactly copy my jumper configuration and try it with your Heath 64K RAM board and see if that gets the board operational.
Just one note regarding the H8 bus and dynamic RAM refresh. The H8 bus carries none of the Z80 DRAM refresh signals, so external DRAM must always refresh itself (in contrast to, say, the H89 where the Z80 directly refreshes the DRAM). I'm not sure what the external RAM board jumper "z80" is for, but it would not be refresh as far as I can tell. SRAM, of course, does not require refresh.
On Oct 22, 2022, at 7:18 AM, Douglas Miller <durga...@gmail.com> wrote:
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“X” is the ROM DISABLE jumper. Per the Rev. 3.1 board instructions: “When jumper inserted drives /ROM_Disable signal into the H8 bus” … “not inserted” for normal operation. I do not have the “X” jumper installed on any of my newer Z80 boards (2.6, 3.1, 4.0) and they operate fine under HDOS and CP/M, CP/M3, etc.
So there does seem to be a conflict in the instructions between the 2.6 (p. 14, step 7.2) and later boards. For just seeing if the board comes up at power-on either position seems to work.
On the 8080 when you upgrade to the HA-8-8 “extended configuration” (ORG zero) board the instructions say to insert the “X” jumper…
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I will send you a pcb 64K board by weekend as your WH8-64KB board is kind of non-operational with the Z80. It must be a timing issue on such board.
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On Oct 24, 2022, at 11:51 AM, Joseph Travis <jtravi...@gmail.com> wrote:
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Awesome outcome Joe!
Next you should be able to try out the speed board! Documentation and speed utility are on Norberto’s site
but you can also use the front panel to change the CPU speed. Output 0, 1, 2 or 3 to port 220Q to set the speed per the following table:
If you haven’t modified the front panel the display LEDs won’t refresh properly at higher speeds (though the OS should work fine). My preferred solution is to put a 2.048 Mhz oscillator right on the FP board. I documented this a while back with some pictures:
but there were also other workarounds (I think this is discussed on Norberto’s site).
If you have the new front panel from Norberto this already has the fix built in…
Let us know when you’re flying at 10 (or 16?) Mhz!
Thanks. Obviously more current than my older information.