I'm experimenting with a few libraries that allow me to talk to an AutomationDirect 05 PLC. I want to read the state of the hardware inputs (photo eyes, etc.) and set the state of the outputs (relays, etc). But I'm confused by the PLC terminology and can't find a clear definition. Which would I be concerned with reading/writing?

Read Coil / Read Discrete Input / Read Holding Register / Read Input Register

Write Coil / Write Holding Register

I guess I'm not clear on the relationship between these terms and how they relate to the physical hardware inputs/outputs. I should note that my 05 PLC had its memory cleared by AD, so do I have to do anything to get up and running, like map the inputs/outputs to memory addresses or is that already a given?

Thanks in advance, I come from a Windows background, so this PLC stuff is new to me.

 

Read/Write Coil = read/write a binary data point
Read/Write Holding Register = read/write integer data

I would focus on those four, in ADirect terms binary data = Cxxx and integer data = Vxxxx. The Adirect manuals cover this pretty well. Look in the CPU chapter.