Limit on daisy-chaining parallel port devices?

Discussion about old PC hardware.

Limit on daisy-chaining parallel port devices?

Postby snorg » 2018-9-16 @ 17:48

Lots of parallel port devices/drives have a pass-through port so that you can use the drive with another parallel port device.
Which makes me wonder, is there a limit on how many you can daisy-chain this way? I know with SCSI you could do seven devices but SCSI was designed for that, the parallel port (as far as I know) was only ever meant for printers and was adapted for other uses. So I imagine you could do at least 2 but I would be curious what the limit is. Anyone out there have several LPT devices hooked up like this?
snorg
Oldbie
 
Posts: 999
Joined: 2011-5-29 @ 15:32

Re: Limit on daisy-chaining parallel port devices?

Postby derSammler » 2018-9-16 @ 18:08

There is no limit, since daisy-chaining was never intended. The port is designed for a single device. Daisy-chaining works until the voltage drops below the point where the other side can no longer distinguish between TTL high and low.
derSammler
Oldbie
 
Posts: 1779
Joined: 2017-4-14 @ 11:30
Location: Germany

Re: Limit on daisy-chaining parallel port devices?

Postby snorg » 2018-9-16 @ 18:51

derSammler wrote:There is no limit, since daisy-chaining was never intended. The port is designed for a single device. Daisy-chaining works until the voltage drops below the point where the other side can no longer distinguish between TTL high and low.



Ok, so there is no set limit as such, but would it be fair to say a practical limit is maybe 2 or 3 devices?
snorg
Oldbie
 
Posts: 999
Joined: 2011-5-29 @ 15:32

Re: Limit on daisy-chaining parallel port devices?

Postby ibmapc » 2018-9-16 @ 19:06

I think you would be limited by the types of devices chained together as well. You would not be able to use more than one of a particular device type. I.E. you won't be able to chain two Parallel Zip drives or anything that uses the same resources.

Greg.
User avatar
ibmapc
Newbie
 
Posts: 27
Joined: 2018-1-26 @ 19:02

Re: Limit on daisy-chaining parallel port devices?

Postby Zup » 2018-9-16 @ 19:12

I think that the limit is TWO devices, and one of them must be a printer.

I've only seen passthrough ports in external drives and scanners, but I don't think that you can chain two of those bidirectional devices.
I have traveled across the universe and through the years to find Her.
Sometimes going all the way is just a start...

I'm selling some stuff!
User avatar
Zup
Oldbie
 
Posts: 1163
Joined: 2003-10-04 @ 12:16


Return to General Old Hardware

Who is online

Users browsing this forum: Bing [Bot], luckybob and 5 guests