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Appendix A.2. Data Types
Each produced data packet contains up to 1400 bytes of unstructured data. The specification of the ge_data_type in the Map Descriptor tells the driver how to interpret these raw data bytes.
The minimum data unit processed is a byte. This is the case even when the data type is specified as bit. This is because EGD producers cannot produce a single bit. When bits are produced the producer determines the closes byte boundary and sends a minimum of 8 bits.
The following data types are recognized by the driver
Byte |
|
Bit | (translated as 8bits aligned with a byte boundary) |
Word | (unsigned 16bit integer) |
Dword | (unsigned 32bit integer) |
Int | (signed 16bit integer) |
Long | (signed 32bit integer) |
Float | (translated as an IEEE 4 byte real number) |
Double | (translated as an IEEE 8 byte real number) |
The following GE Specific data types are also recognized.
Type | Description |
%R | Register memory in word mode P/C |
%AI | Analog input memory in word mode P/C |
%AQ | Analog output memory in word mode P/C |
%I | Discrete input memory in byte mode P/C |
%Q | Discrete output memory in byte mode P/C |
%T | Discrete temporary memory in byte mode P/C |
%M | Discrete momentary memory in byte mode P/C |
%SA | Discrete system memory group A in byte mode P/C |
%SB | Discrete system memory group B in byte mode P/C |
%SC | Discrete system memory group C in byte mode P/C |
%S | Discrete system memory in byte mode P |
%G | Discrete global data table in byte mode P/C |
If you use the RUI editor and view the Map Descriptors online it may appear that the driver changed the data type but in fact all that it has done is changed the display to a synonym.
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