Quick question about parallel ports

A

awdark

[H]ard|Gawd
Joined
Mar 22, 2003
Messages
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Im going to be getting some parallel lcds from the BST section here and I was wondering if its possible to wire a printer and lcd in parallel on the same parallel port.

I know my scanner used to have a pass through thing and im hoping I could connect my printer and lcd at the same time. Logical or puff of smoke?
 
I doubt it will work.. but what do I know..nothing that is

why not get a USB cord for your printer!
 
No puff of smoke but unless you have some sort of software to tell the port which device you want to talk to either the printer or LCD will do funny things. Not that it will matter though. As long as you don't use the printer all that much and leave it off when you don't need it and just put up with a wonky LCD during and after printing it should be fine. Having too many devices connected may result in not enough signal making it out of the port to do anything.
 
You should really use something like this:
http://www.wellspent.org/Product?p=216878

The whole idea of a parallel bus is to have multiple devices connected on it. The only problem is that most busses also have a "chip enable" pin going to each device. I doubt that a printer leaves any pins unused, so you can't go this route. Just use a parallel switch.
 
I picked up a parallel switch at a used electronics place for $2.95, works great, switches all 25 pins, mechanically. You might look into one of those.
 
You could also get an LPT to USB adapter for your printer. It wouldn't work for your LCD, though.
 
I see, its a oold epson 700 that still works quite well. I might look into one of those USB adapters or the switch boxes.

Hmm if I had the LCD and the printer on the same port, I wonder if it woudl drive the printer nuts :p
 
awdark said:
I see, its a oold epson 700 that still works quite well. I might look into one of those USB adapters or the switch boxes.

Hmm if I had the LCD and the printer on the same port, I wonder if it woudl drive the printer nuts :p
Click to expand...

undoubtedly
 
i'd think it'd depend completely on the software... i had a zip drive and printer daisy chained for the longest time with no problems back in the day...
 
plot said:
i'd think it'd depend completely on the software... i had a zip drive and printer daisy chained for the longest time with no problems back in the day...
Click to expand...

Were you able to use both devices at the same time?
 
plot said:
i'd think it'd depend completely on the software... i had a zip drive and printer daisy chained for the longest time with no problems back in the day...
Click to expand...

Were you able to use both devices at the same time?
 
Parallel zip drives were designed to be daisy chained though, that's why they had the printer port on them.

His equipment is not designed to work like that.
 
rm.o said:
Parallel zip drives were designed to be daisy chained though, that's why they had the printer port on them.

His equipment is not designed to work like that.
Click to expand...

he could design it to work like that though as he's the one wiring up the LCD.



and i was able to print stuff from the zip drive.. so i guess they both worked at the same time.. (well, obviously they couldnt work at the same time, but no noticable delay)
 
ahem....

i have been working on a circuit which will (hopefully) do exactly this. i would have to look into how many control lines the printers use though...

here's something i posted on another forum, in hopes that i could find some software gurus and also hardware experts to help me a bit...

i would like to be able to build a circuit that allows 2 or more devices to be controlled at the same time with the same parallel port... i.e.- a hd44780 character lcd and an led display, (or whatever).
i don't have any experience with programming, so i'd like the whole project to be primarily hardware based. if possible, soley hardware based!

here are some of the thoughts i have had so far-

the pins on the parallel port consist of this:
8 data out pins
5 input/status pins
4 control lines
(then the rest are ground pins)

when interfacing the hd44780 to the parallel port, all 8 data pins are used, and 3 of the control lines. BUT, depending on the software used, one of those control lines is not usually used by the lcd.
so, here's what i'm thinking- i can somehow use the 2 left over control lines as device selectors (with some 74HC latches or gates). i.e.- maybe there could be x number of devices at one time, each having it's own gate or latch.
when one device is selected, the output is enabled on it's latch, and the data from the parallel port will reach that device. the other devices will not display the data being sent through the port because outputs are disabled on those device's latches.
does that make sense?
i have also had alot of ideas that i'm fairly sure would work well, but they would rely heavily on software.
 
:eek:
Thats an interesting idea but I think it would be easier to write a program that allows for multiple connected devices though...
 
awdark said:
:eek:
Thats an interesting idea but I think it would be easier to write a program that allows for multiple connected devices though...
Click to expand...

Easier for people that know how to program.
 
yes soo true.. It was more of a camouflaged bump in hopes that circuit idea will get some attention.

So that idea... it will switch all the wires to the next set of wires depending on printer vs lcd?
 
Kerri Ann's idea is a good one.

Just hurry up and connect them both at once. I want to know what happens!
 
What mode do lcds use on the parallel port? that EPP ECP or SPP mode? or some mix of it?
 
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