Question:
What are the Words and DWords formats in Siemens’s PLCs (S7-200, S7-300, S7-400, S7-1200, etc.)?
Solution:
In Siemens’s PLCs, the Word0 (MW0) comprises Byte0 (MB0) and Byte1 (MB1), in this exact order.
Example: MW0 = MB0 & MB1 (MB1’s bits are MW0’s least significant ones, while MB0’s bits are MW0’s most significant ones).
The same thing goes for Double Word0 (MD0), which comprises Word0 (MW0) and Word1 (MW1).
Example: MD0 = MW0 & MW1 (MW1’s bits are MD0’s least significant ones, while MW0’s bits are MD0’s most significant ones).
The figure below illustrates how to assemble Words and DWords:
