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Re: 486 board with UMC 8881E/8886B: The winner is: EDO without L2 (if your only other option is L2 at 3-2-2-2)

Posted on 2025-05-18, 17:51

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

The PCI speed is 25 MHz because, as you posted in another thread, the 2/3 output is is misshapen, as if it has a duty cycle that is not 50%. Exactly. Maybe I can find a PCI graphics card that doesn't care about the wrong duty cycle, and use the 2/3 divider. Could the PCI clock be provided in some …

Re: EtherDFS - a network drive for DOS

Posted on 2025-05-18, 16:14

in Release Announcements

in Release Announcements

Hmmm... Can't you simply enforce FAT32 (or VFAT?) drives being used in Linux for mounted folders and request the short filename path from the driver? Obviously, but who wants to force themselves to format their archival hard drives to FAT32? I certainly don't :P In the case you use a modern Linux …

Re: 486 board with UMC 8881E/8886B: The winner is: EDO without L2 (if your only other option is L2 at 3-2-2-2)

Posted on 2025-05-18, 13:46

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Got the A19 line soldered back in, and fixed it with super glue as strain relief this time. The system still works with at 3-1-1-1 at FSB50. But I got one step faster! If I disable "early cache write mode" in the CMOS setup, the performance at a given cache timing setting does not drop (at least …

Re: XT PC - using a 16 bit video card in 8 bit slot - which cards work ?

Posted on 2025-05-12, 23:38

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Next problem, its not recognising the keyboard. Are you aware that PC/XT keyboards and AT keyboards use different protocols, yet have the same 5-pin DIN plug? An AT-only keyboard will not work on an XT . Some keyboards from the late 80's / early 90's have a switch labelled "X/A" (XT / AT) or 8088/ …

Re: XT PC - using a 16 bit video card in 8 bit slot - which cards work ?

Posted on 2025-05-12, 21:44

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

https://postimg.cc/HjNPg1tM Which one should I use? I think 5 and 6 should be OFF right? Both should be ON. The description is confusing. All combinations except "both ON" activate the video support built into the mainboard BIOS. The mainboard BIOS only supports CGA and MDA video cards. For all …

Re: CL GD5422/20 vs 8900c on 386

Posted on 2025-05-12, 21:40

in Marvin \ Video

in Marvin \ Video

The 5420 is 16 bit memory interface, the 5422 can do 32 bit. It's possible the 5420 may gain something from banked 16 bit Well, the data book is confusing there. At some locations, it claims "5420 has a 16-bit memory interface". At other locations, it limits this claim to the "A" revision. The …

Re: Gigabyt GA-486AM/S : BootBlock and BIOS flash error

Posted on 2025-05-12, 20:34

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

It is probably not the ram sticks that are the cause of all that. But RAM might play an important role here. As everything seems to point towards something wrong with the RAM : let's test it ;-) I made a boot floppy of Memtest v1.11, and the system booted with it. I ran the test with 2 x 16MB FPM …

Re: Monitor ega ?

Posted on 2025-05-12, 20:30

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

The schematic part you show clearly indicates that the monitor is able to take a 6-bit digital RGB input, just like EGA. I don't know whether it supports synchronizing to 21.8kHz, as is required for EGA operation.

Re: CL GD5422/20 vs 8900c on 386

Posted on 2025-05-12, 20:27

in Marvin \ Video

in Marvin \ Video

Both Cirrus chips hit the ISA speed limit. [...] BTW, note that both your Cirrus cards only have 512 KB of RAM - it doesn't make sense! They are well worth upgrading to full 1 MB. Using the Cirrus cards with only 512KB of RAM halves their memory bandwidth. I'm unsure whether they still manage to …

Re: Gigabyt GA-486AM/S : BootBlock and BIOS flash error

Posted on 2025-05-11, 23:17

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

The main problem is the BootBlock... i.e., what's preventing the BIOS from working properly? On your system, the boot block is always executed first when you turn on the computer. The boot block is supposed to not be erased when the BIOS is upgraded in-system, and it has one primary purpose: …

Re: Gigabyt GA-486AM/S : BootBlock and BIOS flash error

Posted on 2025-05-11, 20:45

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I have tried different memory configurations to no avail... Memory might still be the key to the issue. Unless a 486 board has the very latest revision of the UMC 8881 or SiS 496 chipset, it does not support EDO RAM . If you started computer stuff around the time the Pentium 133 was common, it is …

Re: 486 board with UMC 8881E/8886B: The winner is: EDO without L2 (if your only other option is L2 at 3-2-2-2)

Posted on 2025-05-10, 11:48

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I had clicked "Download Zip" from this page, but it did not contain JLCPCB gerbers. This is the zip I had been uploading to JLCPCB which didn't work. Shown here: Github_screenshot_1.png I'm sorry for that misunderstanding. I tried to avoid that by directly linking the v1.1 release page in my last …

Re: Obscure enhanced CGA clones with 640x400 monochrome mode

Posted on 2025-05-10, 07:50

in Marvin \ Video

in Marvin \ Video

The line-doubling helped to be able use a single monitor frequency, I assume. I don't think this is the primary reason. Both CGA and the Apple II used NTSC video output, so plain CGA and Apple II match up perfectly at the same monitor frequency of around 15kHz. On the other hand, this computer …

Re: 486 board with UMC 8881E/8886B: The winner is: EDO without L2 (if your only other option is L2 at 3-2-2-2)

Posted on 2025-05-10, 07:40

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

When you uploaded these zip files (v1.0 or v1.1) to JLCPCB, did you see "Detected 0 layer" and notice that Gerber Viewer cannot open? Normally, the website detects the correct layer and Gerber Viewer works. Oh, that's strange. I tried the automation of the Gerber generation on my system before …

Re: What do the Switches on 72-pin SIMMs do?

Posted on 2025-05-09, 21:30

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

That doesn't make sense. I looked closer- the top row of 4 chips has a different part number then the rest. They MUST be buffered/ecc/parity/something like that. Not to say they won't work for you, they may. Just saying that's more then just "regular FPM" Indeed, the top row are 4M x 1 chips (for …

Re: 486 board with UMC 8881E/8886B: The winner is: EDO without L2 (if your only other option is L2 at 3-2-2-2)

Posted on 2025-05-09, 21:07

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Looking forward to this... I just finished https://github.com/karcherm/mb8433-uud-cache-pcb/releases/tag/v1.1 - I hope this suits your requirements. This comes with absolutely *no* *warranty*, as I only tested a prototype of v1.0, but as the current version still passes the built-in checks in KiCad …

Re: Diagnosing Zenith Data Systems ZCM-1495 CRT VGA monitor

Posted on 2025-05-09, 16:36

in Marvin \ Video

in Marvin \ Video

I did not know about such a completely real flat CRT in 1992. Yes, this is in fact quite special. It's Zenith's proprietary "Flat Tension Mask" (FTM) technology. If you are interested, this name might help to get you started on Google to find more information. While competing shadow mask designs …

Re: Diagnosing Zenith Data Systems ZCM-1495 CRT VGA monitor

Posted on 2025-05-09, 16:32

in Marvin \ Video

in Marvin \ Video

It states that it is a VGA monitor but it is constantly out of sync. Yeah, I can confirm that the picture looks like the horizontal sync is not working. If this monitor is a fixed frequency VGA monitor, it's quite likely that the capture range of the horizontal oscillator is quite small. Standard …

Re: Quadram EGAVGA - how to get it into VGA mode?

Posted on 2025-05-09, 16:20

in Marvin \ Video

in Marvin \ Video

Hires "mode 12": Quadram_EGAVGA_hires_hsync.png What you see here is likely cross-talk from the video signal, while the text mode is probably taken with a mostly black screen. The EGA hi-res mode is known for squeezing the horizontal timing as much as possible, i.e. display up to the latest …

Re: SB16 Vibra +1 tone

Posted on 2025-05-09, 06:31

in Marvin \ Sound

in Marvin \ Sound

I'm wondering if your mobo/BIOS settings are using a too high ISA clock. The ISA clock (CLK) and the 14.318 oscillator pin (OSC) on the ISA bus are two different pins. ISA clock adjustment is not supposed to have any influence on the OSC pin. On many modern boards, OSC is driven directly from the …

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