H8 512K RAM MMU V40. R12. 50K or 100K?

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Rob

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Jul 1, 2022, 10:50:50 PMJul 1
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The silkscreen on the ver 1.2 of the board say 50k, the BOM says 100k.

I currently don’t have a 50k resistor, but I do have 100k resistors.

Which resistor should I use?

Thanks!

P.S. I did search for this and only found reference to the version 1.1 of the board.

Rob

Peter Higgins

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Jul 2, 2022, 12:27:34 PMJul 2
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For R12, both the schematic and the board silkscreen indicates 50K. That is what I used and it seems to work fine, but it would be nice to get confirmation from Norberto.

You also need to think about R18. On the schematic and silkscreen it is indicated as 100K, however in several discussions in this forum Norberto has pointed out that when this RAM board is used with the Z80 V4.0 board, R18 should be 50K.

Glenn Roberts

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Jul 2, 2022, 1:54:32 PMJul 2
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I am using the Rev 1.2 MMU board with the Rev 4.0 CPU board (“Big Blue”).  my board has 50K at R12 and 100K at R18.  There is a glitch that I’ve never tracked down on this setup – I am unable to reliably push CP/M 3.0 to 10Mhz – I keep getting repeat “A>” prompts on the screen when I do that.  All is well at 8 Mhz.  also, I can run HDOS 3.0 at 10 Mhz just fine (but then again it doesn’t rely on the MMU board for anything special).

 

I have no idea if these two are related but I would say things are not quite running perfectly with my setup.  Would be great if reducing R18 to 50K would fix this problem!??

 

  • Glenn

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norberto.collado koyado.com

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Jul 2, 2022, 4:08:57 PMJul 2
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When using Z80 V4.x boards, the resistor on the RAM MMU should be 50K as this version of the Z80 board comes out of reset faster than previous Z80 boards. All older MMU RAM should be reworked to have a 50K ohms value. In my board I just soldered another 100K resistor on side 2.

 

As  you have two 100K, solder one on side 1 and then solder the second one  on side 2 in parallel.

 

Thanks,

Norberto

rw...@robhome.com

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Jul 2, 2022, 4:53:19 PMJul 2
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[Image.jpeg]

Two 100k's should do the trick then.

Thanks!

Rob Waggoner
________________________________
From: se...@googlegroups.com <se...@googlegroups.com> on behalf of norberto.collado koyado.com <norberto...@koyado.com>
Sent: Saturday, July 2, 2022 3:08:53 PM
To: sebhc Google Group <se...@googlegroups.com>
Subject: RE: [sebhc] Re: H8 512K RAM MMU V40. R12. 50K or 100K?


When using Z80 V4.x boards, the resistor on the RAM MMU should be 50K as this version of the Z80 board comes out of reset faster than previous Z80 boards. All older MMU RAM should be reworked to have a 50K ohms value. In my board I just soldered another 100K resistor on side 2.



As you have two 100K, solder one on side 1 and then solder the second one on side 2 in parallel.



Thanks,

Norberto



From: se...@googlegroups.com <se...@googlegroups.com> On Behalf Of Glenn Roberts
Sent: Saturday, July 2, 2022 10:55 AM
To: se...@googlegroups.com
Subject: RE: [sebhc] Re: H8 512K RAM MMU V40. R12. 50K or 100K?



I am using the Rev 1.2 MMU board with the Rev 4.0 CPU board (“Big Blue<https://photos.app.goo.gl/zgBugDmBnomjmr4i6>”). my board has 50K at R12 and 100K at R18. There is a glitch that I’ve never tracked down on this setup – I am unable to reliably push CP/M 3.0 to 10Mhz – I keep getting repeat “A>” prompts on the screen when I do that. All is well at 8 Mhz. also, I can run HDOS 3.0 at 10 Mhz just fine (but then again it doesn’t rely on the MMU board for anything special).



I have no idea if these two are related but I would say things are not quite running perfectly with my setup. Would be great if reducing R18 to 50K would fix this problem!??



* Glenn





From: se...@googlegroups.com<mailto:se...@googlegroups.com> <se...@googlegroups.com<mailto:se...@googlegroups.com>> On Behalf Of Peter Higgins
Sent: Saturday, July 02, 2022 12:28 PM
To: SEBHC <se...@googlegroups.com<mailto:se...@googlegroups.com>>
Subject: [sebhc] Re: H8 512K RAM MMU V40. R12. 50K or 100K?



For R12, both the schematic and the board silkscreen indicates 50K. That is what I used and it seems to work fine, but it would be nice to get confirmation from Norberto.



You also need to think about R18. On the schematic and silkscreen it is indicated as 100K, however in several discussions in this forum Norberto has pointed out that when this RAM board is used with the Z80 V4.0 board, R18 should be 50K.

On Friday, July 1, 2022 at 7:50:50 PM UTC-7 Rob wrote:

The silkscreen on the ver 1.2 of the board say 50k, the BOM says 100k.



I currently don’t have a 50k resistor, but I do have 100k resistors.



Which resistor should I use?



Thanks!



P.S. I did search for this and only found reference to the version 1.1 of the board.



Rob

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