Its Perfect!!! Thank you so much! Works great, and much more stable than the program I got. I just have 4 questions, If you have time
EDIT - I did some research (try and burn) and answered 2 answers - hope someone building the parallel port project could find them useful
1. What is a pull up resistor? Something like a ghost load? (The pins have internal pull up resistors)
A pull up resistor is required in cases where the driver ic output pin is open collector, it has not got an internal resistor to Vss, a o/c pullup is about 220R thru 1K0 depending upon the application
Also pull up resistors are used on inputs to ic's in order to pull them to a 'good' logic high, about Vss, an input pullup can be typically from 1K0 thru 10K
In some cases the circuit may require a pull down resistor.
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2. According to the table, some pins have and active low signal, and others are inverted. What does that mean?
here is the answer
https://www.codeproject.com/KB/cs/csppleds.aspx?df=100&forumid=21021&exp=0&select=974134
3. There are 8 "IN" on the port. So, if I want to check the state (i.e.) a microswitch in the window, should I connect any of those pins in series with the microswitch, and then (I guess) any ground?
10 /Ack In
11 /Busy In
12 Paper In
13 Select In
14 /Auto In/Out
15 /Error In
16 Initialise In/Out
17 /Select Prn In/Out
yes! that's the way it works. Refer to the above link for more info
4. Why is necessary to get the buffer? Is not enough to simply connect the port through a diode, and a transistor, to drive the relay?
The PC port drive capability vary from one PC to another, some can supply 12mA and others 20mA at about +3.5V
This is often not enough to drive an external input, so a transistor amplifier is used to supply a higher current to the external load, relay etc.
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Thank you again!