Make sure that the address is valid as follows:

To map a valid address in an application, you have to know the required position (applicable memory range) in the process image: input memory range (I), output memory range (Q), and flag memory range (M) — see above. Furthermore, you have to specify the required size prefix: bit, ‎BYTE‎, ‎WORD‎, ‎DWord‎ (see above: ‎X‎, ‎B‎, ‎W‎, ‎D‎)

The current device configuration and device settings (hardware structure, device description, I/O settings) play a decisive part. Note specifically the differences in the interpretation of bit addresses for devices with "byte addressing mode" and devices with "word-oriented IEC addressing mode". For example, in a byte addressing device, the number before the point of bit address ‎%IX5.5‎ addresses byte 5. On the other hand, in a word-addressed device, it addresses word 5. In contrast, addressing with a word or byte address is independent of the device type: with ‎%IW5‎ always word 5 is addressed and with byte address ‎%IB5‎ always byte 5. Regardless of size and addressing mode, you can address different memory cells therefore with the same address information.

The following table shows the comparison of byte addressing and word-oriented IEC addressing for bits, bytes, words, and double words. It also shows the overlapping memory ranges that are present in the case of byte addressing (see also the example below the table).

Regarding syntax, note that the IEC addressing mode is always word-oriented. In this case, the word number is located before the point and the bit number ofter the point.

n = byte number