Advanced Programmable Logic Controller (PLC) Practice Test

The valid range for the last piece of the I/O tag string's bit number is 0 to 31. This range is significant because it reflects the way that individual bits are identified within a word or register in PLC programming.

In many PLC systems, I/O points are mapped into registers, with each register typically being 32 bits wide. Therefore, the bits within a single register are indexed from 0 to 31. This means that the bit numbers 0 through 31 allow for the identification of each specific bit that can be addressed for processing logic. Thus, using any value beyond this range would be invalid in the context of standard PLC configurations, where operations and control rely heavily on correctly referencing these bits.

Understanding this range is crucial for effective programming and troubleshooting, as addressing issues or setting bit flags will often require knowledge of which specific bit location to reference within the available space of a register.