Simple circuits pdf document coudl not be printed examples to describe how to use PC parallel port as general purpose output port. The PC’s parallel port can be used to perform some very amusing hardware interfacing experiments. The port is very easy to use when you first understand some basic tricks. This document tries to show those tricks in easy to understand way.
O port level controlling details here has proven to work well with parallel ports on the PC motherboard and expansion cards connected to ISA bus. Every reasonable care has been taken in producing this information. Not all 25 are needed always. Those output pins are adequate for many purposes. Pins 18,19,20,21,22,23,24 and 25 are all ground pins.
Those datapins are TTL level output pins. Here is a simple idea how you can connect load to a PC parallel port data pins. This is not the only way to connect things to a parallel port. In ordinary parallel port implementations the data outputs are 74LS374 IC totem-pole TTL outputs which can source 2. 6 mA and sink 24 mA. This is called a “totem pole output”. 5 volts and the output can be energized.
The outputs are designed so that they give at least 2. 6 mA figure is for ordinary LS-TLL circuits used, the LSI implementations used in many computers can give more or less. UM82C11-C parallel port chip can only source 2 mA. When taking current from PC parallel port, keep the load low, only up to few milliamperes.
I have had in cases where too much load has made the parallel port IC very hot. You can connect one circuit to each of the parallel port data pins. In this way you get eight software controllable LEDs. LED is connected, that LED will light.