![]() For example the address P#DB25.DBX 0.0 Byte 14 points to the first byte of DB25 with a length of 14 bytes. To do this, the last pointer method is used to describe an area. Some functions in the library use the ANY data type to work on whole sections of memory. The ANY data type is used to pass a parameter of an unknown or undefined data type. The pointer address may be in three different formats. A pointer is always preceded by a P# symbol. The POINTER and ANY Data TypesĪ POINTER data type is used to format a number to be accepted as an address rather then a value. It is also a method that must be understood to use some of the library and system function calls provided by Siemens. While this may increase the difficulty of troubleshooting, its advantage is to greatly reduce the number of networks and instructions needed to control a process. In this case, a memory location stores a “pointer†to another memory location. The following are examples of direct addressing:īy using the methods of indirect addressing the address used by an instruction can be varied to point to any number of locations. ![]() When a direct addressed is referenced by an instruction there is no question as to the location in memory. The most common form of addressing used in the Siemens S7 PLCs is direct and symbolic. Check out their website for hands-on and online training classes. This is a really nice explanation of a difficult but important subject. The following is provided by Automation Training from their excellent Siemens Step 7 training manual. ![]()
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