S-Video vs. ADB switch

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Tom Owad's picture
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I'm thinking about getting an S-Video switch like this to use as an ADB switch (swapping keyboard and mouse between two computers).

Anybody ever try this? I've hot-swapped plenty of keyboards by hand without having any trouble. I'm mostly wondering what really goes on inside one of these boxes. Is it a clean completely-disconnect-from-the-first then connect to the second?

Even if they're both connected momentarily - I'll have both the systems plugged into the same power strip, so they'll have the same ground. Is there any potential harm here?

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I am not sure if the pinouts

I am not sure if the pinouts are the same between the two. I think they are both straight through, but would be worth a check to verify that. I have had a few machines lockup on me when doing keyboard swaps, but these where systems running system 7. I havent ever tried it with os8 or os9. Being that an electronic switch, it just uses relays inside to switch between inputs most likely. If I was the one programming the controller, I would have made the current one turn off before turning on the next one. Basic common sense. But for 10 bucks, its worth a try Wink

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Re: S-Video vs. ADB switch

Tom Owad wrote:

Is there any potential harm here?

It depends on the type of switch it is. If it's a "soft" switch, where it pads the outputs while making the switch, you should be okay. If it's a "hard" switch, where it just plain cuts one out and cuts another in, could potentially cause harm to the machine the swtich is plugged into...a hard swtich could do the same thing just unplugging and replugging an ADB device could (that is, potentially kill the ADB controller).

I've seen ADB switchboxes in the past...perhaps a post to the LEM Swap List would be a good idea to find one.

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Re: I am not sure if the pinouts

Stuka wrote:

I am not sure if the pinouts are the same between the two. I think they are both straight through, but would be worth a check to verify that. I have had a few machines lockup on me when doing keyboard swaps, but these where systems running system 7. I havent ever tried it with os8 or os9. Being that an electronic switch, it just uses relays inside to switch between inputs most likely. If I was the one programming the controller, I would have made the current one turn off before turning on the next one. Basic common sense. But for 10 bucks, its worth a try Wink

Svideo cables will work for ADB but ADB cables will not always work for svideo. The reason is ADB cable grounds are not shorted to the shell and svideo is. This is to sense when the cable is connected.

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coius's picture
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I beg to differ.....

Quote:

Svideo cables will work for ADB but ADB cables will not always work for svideo.

I beg to differ. I have tried ADB cables as an S-Video cable and I can testify that it will work... It just has a fuzzy image because there is not enough shielding and the wires are of poor quality.

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Tom Owad's picture
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But [i]is[/i] there really an

But is there really any harm in a hard ADB switch? I thought the concerns with hot-swapping ADB was that you might misalign the pins and short something out.

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Which wires get switched in an S-vid switch?

Are they the same ones as need to be switched for ADB? Are any circuits shorted to ground?

I suppose the best way to find out is to drop the $20 (total) and check it out yourself. Since ADB switchers are scarce and/or $$$ it's certainly an intriguing idea.

As for ADB being vulnerable, I've swapped so many live ADB stuff over the years and have never fried anything. I can't say however what would happen if you directly short any of the lines. I'd suggest it's better to not use any device which would short any of those circuits.

dan k

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Re: I beg to differ.....

coius wrote:
Quote:

Svideo cables will work for ADB but ADB cables will not always work for svideo.

I beg to differ. I have tried ADB cables as an S-Video cable and I can testify that it will work... It just has a fuzzy image because there is not enough shielding and the wires are of poor quality.

Uhm... did you not read his post? He said "Svideo cables will work for ADB but ADB cables will not always work for svideo." as in... some may work, some may not. He didnt say no ADB cable will work period.

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pointer slow down switching ADB in OS X

I run OS X on 2 legacy machines (via XPostFacto)...

What I have noticed, and it is consistant, is that when I remove the ADB mouse, then plug it back in, it always moves at the slowest movement setting, even when the Mouse setting is set higher.

I'm not sure if this is worth noting or not, but I have rebooted just for the sake of getting my mouse settings back. I imagine a switch would accomplish the same problem.

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Re: I beg to differ.....

coius wrote:
Quote:

Svideo cables will work for ADB but ADB cables will not always work for svideo.

I beg to differ. I have tried ADB cables as an S-Video cable and I can testify that it will work... It just has a fuzzy image because there is not enough shielding and the wires are of poor quality.

My first year at apple we tested the svideo output on powerbooks with an ADB cable. It worked great most of the time, except when the machine tried to sense the presense of the cable, which it was not wired correctly for.

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Re: But [i]is[/i] there really an

Tom Owad wrote:

But is there really any harm in a hard ADB switch? I thought the concerns with hot-swapping ADB was that you might misalign the pins and short something out.

The harm of hot swapping is caused by power flowing on the data lines when the cable is yanked. You'll notice connectors designed for hot swap have a few pins that are longer than the rest. These pin are power and ground (and sometimes device presence sense). This way data cables are only connected after power and ground have stabilized.

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Tom Owad's picture
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Chances?

Is ADB bidirectional? I recall there was a shareware app that could play with the keyboard lights, but I can't think of any device that used ADB for output. I'm thinking unidirectional with some sort of clever hack?

Supposing I don't press any keys or move the mouse while swapping, is there really any chance there'll be data on the line?

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Those legacy older ports and

Those legacy older ports and proticols that Apple had tend to be "chatty", so the odds are pretty good that there will be data.

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Tom Owad's picture
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Inside Macintosh

According to Inside Macintosh: Devices:

"In general, the ADB Manager continuously polls the active ADB device, which is the last device that sent new data after requesting service with a service request signal."

So that's bad news for hot-swapping. In a switch, any thoughts on whether the difference in time between the first pin being disconnected and the last pin being disconnected is great enough to be a prolbem?

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it should be greater, not gre

it should be greater, not great enough. Maybe you could pin the data pins down 2mm.

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jt
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ADB Reset . . .

. . . is the answer to speed change issues as well as "lost" ADB devices.

I've been running numerous Macs on an ADB KVM switch (mechanical)for years. There's a shareware (might be freeware, dunno)app called "ADB Reset" that cures almost all ills associated with switching between Macs of different OS revisions, which seems to be the most consistent cause of ADB errors.

jt

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ADB Parser

An Apple utility, found in the developer toolchest section on Apple's older ftp sw server.

Hey jt, nice to see you back!

dan k

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Re: S-Video vs. ADB switch

Hi!

I realize it's been a long time since this thread, but I'm wondering what the best solution is at this point- to switching between 3 ADB keyboards on old Macs.

Without losing the tracking speed of the mouse.

With and without including the monitors included in the switching?

9600, 8100, Beige G3.

OS 8.1
OS 7.6.1
OS 9.2

Thanks for your time!