send event related signal to serial/parallel ports

[David McFarlane]

Estelle,

At 5/31/2010 09:23 AM Monday, you wrote:
>I understand the parallel port communication is faster than the 
>serial port communication.

There is actually quite a bit more to it than that.  I just checked 
my earlier discussion at 
http://support.pstnet.com/forum/Topic2496-8-1.aspx , and perhaps that 
still does not quite answer your question, so I will attempt another 
short explanation here:  A serial port sends a sequence of brief 
pulses over a single wire, using voltages of +12 or - 12.  By 
contrast, a parallel port sends each signal steadily over a separate 
wire, using voltages of +5 or 0.  As you can readily see, these are 
vastly different mechanisms and cannot be easily interchanged.  Else, 
why would we even bother giving them separate names?

>I guess I will have to find a computer with a parallel port since 
>mine only has serial.

Alternatively, note that in another recent thread here we have 
discussed using a commercial USB device to provide digital 
I/O.  However, this would require considerably more code.

As usual, do not take my word for any of this, but look it up for 
yourself.  For those really interested, see the books "Parallel Port 
Complete" and "Serial Port Complete" by Jan Axelson.

-- David McFarlane, Professional Faultfinder

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