Date: 2003-10-09 04:47:59
> -----Original Message----- > From: ext Spiro Trikaliotis [mailto:firstname.lastname@example.org] > 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 http://www.ctips.com/spp.html 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. Message was sent through the cbm-hackers mailing list
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