RE: (slightly OT:) Parallel port question
Date: 2003-10-09 04:47:59

> -----Original Message-----
> From: ext Spiro Trikaliotis []
> Sent: 08 October, 2003 22:20
> To: cbm-hackers ML
> Subject: (slightly OT:) Parallel port question
> Importance: High
> Hello,
> I'm just forwarding this question to the cbm-hackers mailing 
> list, as there
> are some people who might know more about this.
> For the persons on cbm-hackers: This person wants to connect 
> something to
> the parallel port of the PC, using it as an input. He is 
> afraid the parallel
> port could be damaged while the port is put into output mode, but the
> external hardware is connected. 

Well, the solution is simple: drive the port lines with a source that can do three-state.
Have it go hihg-impedance while turned on or reset, and let it go out of high-impedance only when the parallel port is working as input. For example, 74HC541 or 74HC540, depending on whether you need inverting or non-inverting outs.
So I'd probably try to monitor STROBE/, put drivers in high-impedance when active low. Check out the pins at

I'm sure people can suggest other pins to monitor, but the principle is the same: when the host (the PC) says "i'm output", put the drivers in hi-Z. I leave the details of the implementation to you.

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