Re: Sigma Designs EGA cards - a deep dive

Posted on 2020-10-10, 01:04

by

by kdr

in Marvin \ Video

in Marvin \ Video

Wait a second. If the POST sets up some extended configuration register (as I read the datasheet, you can not divide the horizontal clock by two using the 400-line register, so it must be something else) to divide the dot clock by two, all software that just uses regular EGA registers will run at …

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Re: Sigma Designs EGA cards - a deep dive

Posted on 2020-10-10, 00:35

by

by kdr

in Marvin \ Video

in Marvin \ Video

Going to your spare osc idea. I saw that on some cards. There are only so many select bits, unless they added another register. If they used the onboard oscillator and clock divided coming out of the sequencer into the ctrc, then I guess they do have a spare ? If it is register compatible, how to …

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Re: BIOS image collection - requests, discussion etc

Posted on 2020-10-09, 23:50

by

by kdr

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

No idea why they included a memory test for the non-EGA card into the EGA ROM POST routine, but they did... On the XT motherboard, you're supposed to set SW5&6 to the "no video card" option when installing the EGA. Those switches tell the XT BIOS not to initialize a video adapter, which means that …

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Re: Sigma Designs EGA cards - a deep dive

Posted on 2020-10-09, 23:31

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by kdr

in Marvin \ Video

in Marvin \ Video

I'd rather leave the PAL well enough alone and just socket the oscillators. Let's see how the RAM replacement goes first. In the meantime I have the SPEGASYNC installed in my other XT that's running an 8Mhz V20, and that card doesn't appear to require any surgery at all, so the low level EGA fun can …

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Re: Sigma Designs EGA cards - a deep dive

Posted on 2020-10-09, 23:03

by

by kdr

in Marvin \ Video

in Marvin \ Video

When you run the BIOS code in turbo debugger, you might want to just patch the segment for the emulation data from A000 to something inside conventional memory to not depend on the broken RAM in bank 3. You can continue exploring that card in more detail until you get to install the replacement RAM …

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Re: Sigma Designs EGA cards - a deep dive

Posted on 2020-10-09, 22:57

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by kdr

in Marvin \ Video

in Marvin \ Video

Just a few things to mention, since I did similar debugging. On the IBM card's BIOS, it senses the switches and stores the setting in RAM, per the docs. This is the first place I went when I couldn't get the thing to come up as expected on any switch setting. I also probed the switches directly for …

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Re: Sigma Designs EGA cards - a deep dive

Posted on 2020-10-09, 19:25

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by kdr

in Marvin \ Video

in Marvin \ Video

Its new to me that its possible to select the base adress of a EGA card. If you like to use 2 cards at once you also have to select another RAM segment for the 2nd one? Well, first problem is that both EGA cards' address decoders will select their ROM for the C000 segment - I think this means you …

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Re: Mysterious XT keyboard issue with extended keyset

Posted on 2020-10-09, 12:11

by

by kdr

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

First off, an XT system doesn't have a keyboard controller as such. It's basically just a shift register hooked up to Port A of the 8255 PPI chip. The BIOS has a handler for IRQ1 (keyboard interrupt) that reads the scan code from the shift register, clears it (to let the keyboard know it can send …

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Sigma Designs EGA cards - a deep dive

Posted on 2020-10-09, 03:32

by

by kdr

in Marvin \ Video

in Marvin \ Video

I've been investigating a pair of ancient Sigma Designs EGA cards that I got a while back from a pile of untested ISA boards. IIMG_20201009_152955.jpg One of the cards (the SPEGASYNC) works nicely in my Turbo XT at 4.77Mhz, but utterly fails in turbo mode at 10Mhz. Both the RAM (120ns) and ROM (?) …

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Re: EGA Video cards - BIOS image collection

Posted on 2020-10-09, 02:26

by

by kdr

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

#16 Manufacturer/Identifier: ERGO480 Chipset: Chips & Technologies CS8240 (82C43x) + Sigma Designs L1A2334 BIOS-String: IBM EGA COMPATIBLE.*UNISYS EVC V 1.60 (C)Copyright Sigma Designs, Inc 1985,1986 Status: Bad RAM chip (U6) on M3D0-M3D3 (low 4 bits of plane #3), freezes system during POST Status: …

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Re: EGA Video cards - BIOS image collection

Posted on 2020-10-09, 02:07

by

by kdr

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

#15 Manufacturer/Identifier: SPEGASYNC-00 Chipset: Chips & Technologies CS8240 (82C43x) BIOS-String: IBM EGA COMPATIBLE.*UNISYS ENHANCED GRAPHICS CONTROLLER VERSION 1.30 (C)Copyright Sigma Designs, Inc 1985,1986 Status: Working at 4.77Mhz IIMG_20201009_145052.jpg IIMG_20201009_145128_1.jpg Jumpers/ …

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Re: GLX Player the only XT player ? Check Mod Master...

Posted on 2020-10-09, 00:16

by

by kdr

in Marvin \ Sound

in Marvin \ Sound

I use 48KHz as output to stress/Test the mixing speed, of course there is no guantee that the sound is really better. It may be much more improved by using the 16Bit mixing code at a lower output frequency. What about mixing 16-bit samples at 22khz and then outputting at 44khz using dithering to …

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Re: Retro Hardware Collecting rants

Posted on 2020-10-08, 23:51

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by kdr

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

well... don't ask me how the plastic didn't shatter. I unscrewed the frame and snapped it back together, but I can hear loose parts inside will have to take a deeper look :c ...would have been in really good condition too. Nooooo.... another 1084 bites the dust! I hope you're able to save it. Maybe …

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Re: Heath 150-307-3 Chips EGA/VGA

Posted on 2020-10-07, 10:48

by

by kdr

in Marvin \ Video

in Marvin \ Video

This seems to be your card: https://books.google.de/books?id=gC-DsOtl2MgC&pg=PA226&lpg=PA226&dq=sigma+ega+480+jumper&source=bl&ots=fRXfNhuL1x&sig=ACfU3U1tXiFyAq6t9wfoXbRPMH9y4x4GvA&hl=de&sa=X&ved=2ahUKEwjWqczW76HsAhXBjqQKHYMCChgQ6AEwDnoECAkQAg#v=onepage&q=sigma%20ega%20480%20jumper&f=false Nice …

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Re: Heath 150-307-3 Chips EGA/VGA

Posted on 2020-10-07, 01:38

by

by kdr

in Marvin \ Video

in Marvin \ Video

Z-449 Z-449 (150-0307) SwitchType: EGA/ZDS 480 Line Mode Controller: Output Port(s): 15-pin analog 9-pin TTL Compatibility: MDA, HGC, CGA, EGA, VGA Video Memory: 256K only Max. Video Mode Resolution: 640 x 480 x 16 - ZDS Mode 132-Column Support: No Switches: See Below 1 2 3 4 Monitor Type OFF OFF …

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Re: 486 post-repair PS/2 Keyboard protocol issue

Posted on 2020-10-03, 22:55

by

by kdr

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Some quick thoughts: The keyboard controller has a long history of being used as a "miscellaneous control" device: A20 gate, fast reset, etc. It's not uncommon for the keyboard controller to also be involved in the turbo mode control logic. I would place good odds that the periodic activity you're …

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Re: Saving a Cirrus Logic 5428

Posted on 2020-10-02, 23:56

by

by kdr

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

The question here to ask is: Is there any VL-Bus VGA card that doesn't come with its own osilator and uses OSC from the ISA bus? I have dozens of them and every single one has one. That's good to know, thanks for the correction. [My current 486 machine is a HP Vectra VL2 that has a CL-GD5428 on the …

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Re: Saving a Cirrus Logic 5428

Posted on 2020-10-01, 23:29

by

by kdr

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Interesting that this card carries its own 14.318180Mhz oscillator instead of using OSC from the ISA bus. Perhaps there are signal integrity issues with OSC on some motherboards? [The GD-542x series has a PLL for generating all the various video and memory dot clocks from the single 14.318180Mhz …

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Re: Bought these (retro) hardware today

Posted on 2020-09-30, 11:04

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by kdr

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Went to pick up a dead Turbo XT machine today and ended up with a bonus 486SX/25! The 486 was suffering from a case of bad Varta and also had a blown tantalum on the -12V rail that was shorting out the PSU. Patient was rushed into the operating theatre for immediate Vartasectomy and vinegar cleanse. …

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Re: turbo button speed

Posted on 2020-09-29, 00:59

by

by kdr

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

As everyone has already mentioned, there's no "standard" way to implement the turbo/non-turbo mode functionality. For example, the VLSI VT82C486 chipset (for 486DX and 486DX2 class CPUs) has this to say about its implementation: TURBO/NON-TURBO MODE CONTROL It has become standard for fast PC/AT- …

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