No... CGA/EGA signals are TTL while VGA is Analog so it requires more than just a cable.
Quite possible--in fact, several VGA-capable monitors came with not 15 pin HD connectors, but regular DE-9s.
Yes, but they still sent the Analog VGA signal thru the 9 pin connector. You know that a CGA/EGA signal is not Analog. The multisync monitor switches its signal handling from TTL to Analog accordingly.
Stone, your answer is less correct than Chuck's. Note that the OP's question was this:
The sbc also has a 9 pin connector labeled "ext monitor." ... is it possible to convert cga/ega/??? to 15 pin vga with just a cable?
Emphasis on ???.
Zeos asked if it's
possible to connect something that could be CGA or EGA
or something else to 15-pin VGA (i.e. to a DE-15
VGA connector).
It is possible for some value of ???.
It is possible if that 9-pin connector is actually a VGA-compatible analog video connector. You're making the assumption that it's not, and that's jumping to conclusions.
However, I think zeos' original post was also somewhat confusing.
Let me ask you, zeos, to clear things up:
1. Do I understand you correctly that you are talking about
two 9-pin
D-sub (DE-9) video connectors, one the SBC, and one on what we think is an add-on TIGA video card?
2. You say that that Tandy VM-3 monochrome monitor was "the monitor" that was used with this system. Especially if there are two DE-9 connectors, do you know which connector that monitor would have been connected to before its cable connector got cut off? (Either connector? Or if only one, then which?)
3. I'm assuming you suddenly mentioning that
there are five wires means you counted that number of wires in the VM-3's monitor cable whose connector was cut off. (You might have wanted to make that explicit.)
I can show you
a pinout for a monochrome monitor that only requires five wires – however you don't make it clear whether your VM-3 monitor has a cable that's moulded to the monitor at the monitor end, or whether the cable is detachable at both ends.
(Smart questions; others don't see what you see; the most pernicious assumptions are the ones we don't know we're making, yadda, yadda, yadda.) If it's detachable at both ends, then depending on whether you know the pinout of the connectors at the monitor end
(DE-9 again? Something else?), it might be relatively easy to figure out which wire is which, and thus re-attach a suitable DE-9 connector to the cut end while referring to the aforementioned mono TTL pinout diagram
(trusting that the TIGA or SBC DE9 pinout is the same as the aforementioned mono pinout, which is probably but not necessarily true) and using a simple continuity tester/multimeter. If the cable is moulded at the monitor end, and if you don't have the bit that was cut, then it might be significantly harder to figure out what's what, and I am not knowledgable enough to help you with that. Maybe someone else here might.
(Maybe the GND at least is identifiable with a multimeter. Maybe there's some kind of in-cable colour-coding that I don't know but that someone else does. Maybe you'd have to open the monitor and figure out where things go.)
4. I do know that VGA signals can be fed through DE-9 connectors, and I have built
just such an adapter (because I have a VGA video cable with DE-15 on one end and DE-9 on the other – my adapter undoes that DE-9 end back to DE-15
; also shown: a DE15-RJ45 converter box, because even that's possible).
You can do that because VGA
requires just R, G, B, their returns, H, V, and GND. See
the pin out section in the box here. However, the later VGA
I²C/
DDC features occupy some of the other 15 pins on a DE-15 connector, so don't expect plug-and-play monitor/resolution recognition to work across a DE-9 connector. (NB: Not all VGA cables are strictly alike. Test as required.)
It
might be possible to feed monochrome VGA through just five wires by only using G and G-return, leaving out R, B, R-ret and B-ret.
Maybe it's even possible to just connect all the returns to the ground, and if the shielding is connected through and equals ground and/or if the monitor and computer share a common ground, then
maybe five wires might suffice for R, G, B, H, V. But I don't know that for sure, and it'll probably cause image ghosting, might even cause equipment damage and/or a fire hazard, and in any case, I seriously doubt that that's what your five wires were for.
5. If your only concern is connecting that VM-3 monochrome TTL monitor, why even ask about 15-pin VGA? Was it because you thought that VM-3 was some kind of VGA monitor? Or do you think that one of the two DE-9 connectors (see (1)) is a VGA connector and one is a TTL connector? (I'd say that's possible, but I don't know.)
6. Your images are pretty unhelpful. The printed info isn't legible and thus not googleable. And is the VM-3 a portrait monitor? The resolution in
Xacalite's link suggests that it's a landscape mode
close to 4:3, but the pixels may not be square, so it could still be a portrait monitor.
7. There are some
crazy hacks that might allow connecting a TTL video board to a VGA CRT, but unless you know exactly what you're doing, you probably should attempt this, and it might damage your hardware. Anyway, especially an odd-resolution portrait monitor may not allow you to just connect a run-of-the-mill VGA or TTL monitor to the connector that it, the former, was hooked up to – in case that's what you were planning to do. Very unlikely to work.
(And please, zeos, use some punctuation. Your questions are confusing enough, and your "there is another card" paragraph took me a double-take.)
PS:
8. I spy with my little eye two D-sub connectors on your SBC. So is the DB-25 connector a serial port? If so, is there maybe a chance that you could hook up a simple terminal (emulator) to a serial console on that port? (That might be easier.)
