Data conversions

Before data transmitted from a processor can be used by a Windows application, it must be converted into a form suitable for the application. The conversion methods used for polled and unsolicited data collection modes are similar, but are not identical.

Processors store data in their memory as a series of bytes. A data type specification tells a program, either in the processor or in a device communicating with the processor, how to interpret these bytes of data.

In PLC-5 processors, the file type (the letter used in front of the file number) determines the data type specification. For instance,

T4:0

specifies that bytes starting at that memory address are interpreted as members of a timer. The file type is

T

, the file number is

4

, and the element is

0

. The processor determines the physical location of the timer data storage. If the address is specified as

A4:0

, the bytes are interpreted as ASCII data.

The data itself is no different if the file type is

T

or

A

. The only difference is how the software interprets those bytes. The software displays the same data within the bytes differently depending on the file type. For example, if the file type is specified as a timer, the data displays as a number. If the data is specified as ASCII data, it displays as a series of letters and numbers (whatever the data corresponds to as ASCII values).

When programming a processor, if the file type specified does not match the type associated with the file number, the programming software signals an error and prevents that entry. With RSLinx Classic, however, the differences depend on the data collection mode (polled or unsolicited).