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MicroLogix 1200 controllers built-in I/O are considered "Slot 0" in the memory map. When you select the Controller type in RSLogix 5000, the I/O memory locations for the MicroLogix 1200 are pre-defined.
You specifically mentioned the 1762-L24BWA controller. The "B" indicates that the controller has 24V DC Inputs, the "W" indicates Relay outputs, and the "A" indicates 120V AC power.
The "24" indicates 24 total I/O; this controller has 14 Inputs and 10 Outputs.
The wiring can be a little tricky, with mixed common groups and so forth. Print out the Wiring Diagram from the Installation Instructions or User Manual and have it handy whenever you terminate a wire.
The memory addresses of the I/O are I:0/0 through I:0/13 for the Inputs, and O:0/0 through O:0/9 for the Outputs.