what do i need for lpt port interfacing, buffer or pull up? - Electronic Circuits Projects Diagrams Free

spyghost · 25th April 2004, 07:38 AM

i notice a lot of circuits out there that are for parallel port interfacing. there are actually 4 varieties:
- the output lines are pulled up
- the output lines are buffered
- the output lines are directly connected to the other ic's, but there are no buffers
- the outputs are connected to transistors

which of these is "really" the standard way of interfacing the parallel port?

Exo · 25th April 2004, 11:54 AM

It depends on what you want. Do you only need very little current and no safety for the port, connect it directly.

Need more current, then buffer it (with a 74 series buffer for example). Depending on the buffer IC used it might be required to use pullups on the outputs (open collector IC)

Want to completely isolate the port, use optocouplers...

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25th April 2004, 07:38 AM	(permalink)
spyghost	what do i need for lpt port interfacing, buffer or pull up? i notice a lot of circuits out there that are for parallel port interfacing. there are actually 4 varieties: - the output lines are pulled up - the output lines are buffered - the output lines are directly connected to the other ic's, but there are no buffers - the outputs are connected to transistors which of these is "really" the standard way of interfacing the parallel port?

25th April 2004, 11:54 AM	(permalink)
Exo	It depends on what you want. Do you only need very little current and no safety for the port, connect it directly. Need more current, then buffer it (with a 74 series buffer for example). Depending on the buffer IC used it might be required to use pullups on the outputs (open collector IC) Want to completely isolate the port, use optocouplers...