I discovered a discarded SLC-500 unit with chassis & power supply, processor, 4 input cards and 4 output cards. I had SLC programming about 12 years ago in an electro-mechanical class but have not touched it since. I would like to experiment with it but do not know exactly what software is needed and if I have to pay the prices of what the A-B website shows. Also, it looks like I might need the RSLogix software to connect, but I am not sure. This one also has a high $ price on it. Is there a free or cheap program(s) available? Any help will be greatly appreciated.