An internal output is addressed to a bit in the B3 file rather than an address in the output image table. This statement is:

• A. True
• B. False
• C. Depends on the hardware
• D. Not applicable to this PLC

Answer: (A)

The concept being tested is how PLC memory is organized for internal signals versus actual I/O. Internal outputs are stored in internal data files, separate from the I/O image that directly represents the physical outputs. In many PLC architectures, an internal coil or flag is addressed as a bit in a binary data file (such as B3), not as an address in the output image table (O:). The real hardware outputs are driven from the O: image, but the program can first manipulate an internal bit in B3 and then transfer that value into the O: image when you want to actuate hardware. That’s why this statement is true: an internal output is addressed to a bit in the B3 file rather than to an address in the output image table.