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Re^2: Need to detect continuity between 2 terminals

by BrowserUk (Pope)
on Jan 06, 2013 at 21:35 UTC ( #1011921=note: print w/replies, xml ) Need Help??

in reply to Re: Need to detect continuity between 2 terminals
in thread Need to detect continuity between 2 terminals

Those are data communication ports and not general input/output pins

I beg to differ. From the perspective of the code, a parallel port is just a set of 3 registers -- 1x8-bit (data), 1x5-bit(status), 1x4bit(control) -- that can be read and written using the appropriate (INx/OUTx) instructions.

On modern OSs these are privileged instructions, so you do need a device driver that exposes them to application code, but given that access, when the data port is read, any of the data pins (2-9 on a db25 plug) held high will be 1; with those held low as 0.

With an appropriate device driver, this is easily programmed under windows (I've done it). And I read on wikipedia that "On Linux, inb() and outb() can be used when a process is run as root and an ioperm() command is used to allow access to its base address; alternatively, ppdev allows shared access and can be used from userspace if the appropriate permissions are set.".

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Re^3: Need to detect continuity between 2 terminals
by martell (Friar) on Jan 07, 2013 at 20:36 UTC

    I stand corrected. ;)



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