Trixter
Veteran Member
Were they not rated for 60Hz?
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Hercules graphics card question
- Thread starter QuantumII
- Start date
Were they not rated for 60Hz?
Scali
Veteran Member
Nope, MDA uses 50 Hz instead of 60 Hz.
Trixter
Veteran Member
I know MDA *uses* 50Hz by default but what I was asking was whether or not monochrome/phosphor monitors were *rated* for 60Hz. Meaning, if you drove it at 60Hz, would it release the magic smoke, or is that valid?
I think it's valid, since I have a dim memory of watching VCR output on a monochrome monitor with a composite input.
I think it's valid, since I have a dim memory of watching VCR output on a monochrome monitor with a composite input.
Scali
Veteran Member
I think we have to separate two things here:
1) MDA monitors
2) Monochrome monitors in general
MDA is rated at 50 Hz, so technically any MDA monitor only has to work at 50 Hz. All the monochrome monitors I have only work at 50 Hz. Otherwise they would also be capable of displaying CGA (or at the very least sync to a black screen). But I have accidentally plugged my MDA monitors into my clone cards while the DIP switches were set for CGA instead of MDA/Hercules many a time over the years, and all you got was a monitor squealing from not getting into sync (and yes, leave it like that long enough, and it will likely go *poof*).
Clearly there are monochrome monitors around that are not 50 Hz. And if you have a composite input, that input is likely NTSC-compatible, since that is the common standard for composite signals. Which would be 60 Hz.
An obvious example is the PC 5155: it has a monochrome screen, but it is connected to composite CGA, hence it is 60 Hz.
The CRT itself could run at 60 Hz easily, it's just that the control logic in most MDA monitors isn't multisync, so it can't work on frequencies other than the 50 Hz it's hardwired to. With some modifications to the circuit you could probably use them at 60 Hz on CGA.
vwestlife
Veteran Member
It doesn't need to be multisync. 50 vs. 60 Hz refresh rate is such a small difference that it can be easily compensated by adjusting the V-Hold knob on most older monitors and TVs. The IBM 5151 doesn't have a user-accessible V-Hold control, but I'm sure it has a trimpot for it somewhere.
Some monitors and TVs have a wide enough range that if you adjust it just right, you can jump back and forth between 50 and 60 Hz without even needing to touch the V-Hold. (This is useful for my Atari ST, where every time I run a European game or demo, it switches from 60 Hz to 50 Hz video output, and then when I return to the desktop, it switches back to 60 Hz.)
Eudimorphodon
Veteran Member
There were plenty of NTSC compatible green monitors made, not at all rare. (At the time, anyway. The dirt-common Apple Monitor II and /// are NTSC, for instance.) NEC sold a particularly nice one that had a built in amp/speaker and I used to timeshare that between my Model I and the tuner output from an old VCR.
Now, a monitor that has both MDA and composite input... I've never seen one, but I wouldn't be surprised they exist. Princeton Graphics sold a nice dual-frequency mono monitor called the "MAX-12" that did both MDA and CGA in shades of gray, it would have been easy to add composite support if they had wanted to.
Now, a monitor that has both MDA and composite input... I've never seen one, but I wouldn't be surprised they exist. Princeton Graphics sold a nice dual-frequency mono monitor called the "MAX-12" that did both MDA and CGA in shades of gray, it would have been easy to add composite support if they had wanted to.
vwestlife
Veteran Member
My Mitsubishi Diamond Scan AUM-1381 does, but it's color, not monochrome. It has composite, digital RGB(I), and analog RGB inputs, and works with everything from MDA and CGA to Super VGA.
Chuck(G)
25k Member
Yup, got one of those too. I'll go up to 600x800 pretty well.
You mean there's some software for PVC4 to control the emulation modes?
Is it available for download somewhere?
Stone
10k Member
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Scali
Veteran Member
I don't think you need to control anything. Set the dip switches to mono, connect an MDA monitor, and when you run CGA software, it should work automatically... and vice versa.
Just tried it with my PVC4, and nothing.
Software detects it as Hercules, and when forced to use CGA - just blank screen.
If this card has some special emulation features, there must be some software to enable it, something like SMS.COM for ATI GS/SWGS.
Scali
Veteran Member
I don't need any software on my ATi Small Wonder either.
Ah, indeed, ATI SWGS has dip-switches to INDEPENDENTLY select the monitor type and software compatibility.
But if you set the dip-switches to mono monitor (18kHz/50Hz) and CGA software compatibility, then you can't run software written for HGC without calling SMS.COM first, can you?
I've seen plenty of so-called "dual" cards (CGA/Hercules), but none of them was able to guess if software intends to use them as CGA or as Hercules, and I doubt if it's even possible.
Prove me wrong, anybody?
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Scali
Veteran Member
Yup, the software can just override some of the dipswitch settings.
My PVC4 works exactly the same way, it has 4 dipswitches on the back.
I don't think it has a utility to override the settings though... But who knows, it's so similar to the ATi, the utility may actually work
It's a chicken-and-egg problem I guess.
It can work if the user just selects CGA, and the game just sets a CGA mode via an int 10h BIOS routine. A custom BIOS/TSR could say "Hey, apparently I need to switch the card to CGA mode now!".
When a Hercules-specific register is used, you can't detect that with the BIOS, but in theory you could design the card to always switch to Hercules mode, no matter what mode it is currently in.
But if the game tries to be smart and tries to detect which videocard, then it won't work... Because the game would detect the card in its current mode, so if it's in Hercules-mode, it will detect as Hercules, and won't even try to run the game in CGA mode.
So, mystery solved: we have two different PVC4-based cards.
Mine only has 3 switches: one to toggle MONO/COLOR, the other two to set LPT port address.
Concerning autodetection...
There were some "Paradise Autoswitch EGA" cards that claimed to do something like that.
Any idea what was the algorithm? And did it really work reliably? It all looks very tricky and failure-prone to me...
Scali
Veteran Member
Well, I think Hercules and CGA/EGA/VGA can work together quite well.
Namely, IBM chose different base addresses for mono and colour adapters, so that they can both be used together in a single system. So if you program the 6845 on an MDA-compatible card like a Hercules, you use the 3Bxh range, and for CGA/EGA/VGA you use 3Dxh range.
So that can be made 100% reliable.
Well, I've found an old review of Paradise Autoswitch EGA:
InfoWorld - Jul 28, 1986 - Page 53
https://books.google.com/books?id=Vy8EAAAAMBAJ
Looks like there were some problems with the autoswitch feature.
Still an interesting idea though, nowadays it should be possible to figure out a better algorithm and implement it in a virtual machine like Dosbox.
InfoWorld - Jul 28, 1986 - Page 53
https://books.google.com/books?id=Vy8EAAAAMBAJ
Looks like there were some problems with the autoswitch feature.
Still an interesting idea though, nowadays it should be possible to figure out a better algorithm and implement it in a virtual machine like Dosbox.
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Scali
Veteran Member
I think that idea is inherently flawed. On a real machine it is possible to have an MDA/Hercules and CGA/EGA/VGA card working together at the same time, as a dual-monitor setup. So technically it's never a situation of either-or (which might be the reason why IBM never chose to make CGA/EGA/VGA support MDA/Hercules-compatible modes).
There is some software out there which uses such a setup (eg SoftICE... there's also an 'easter egg' in the Stars demo by NoooN: if you have an MDA display connected, you can play a game of Snake/Nibbles on that screen while the demo runs on the VGA screen).
If you're making a virtual machine, you should just emulate both (similar to how DOSBox wrongly treats composite CGA as a separate 'mode' of the CGA card. It's not, composite and RGBI signals are active at the same time, and you can connect both monitors together. What you see depends on which monitor you're looking at, not any kind of settings on the CGA card).
You mean you can't set mode 7 on a genuine IBM VGA? Works fine with all (almost all?) VGA clones.
Indeed, I used to use such a setup with stuff like Turbo Pascal and Turbo Debugger, and I accidentally discovered that Scorched Earth game displays some debug messages on the secondary monitor.
BTW, while we're at Hercules and demos: ever seen a demo for HGC graphics mode? Back in the era I heard some rumors about one, but never found it...
True, the virtual machine should have an option to create three windows: MDA, CGA RGBI, CGA Composite.
But there's still a problem with Hercules: some software uses the second video page which conflicts with CGA.