Memory Tags
Memory tags reside exclusively in the OPC Server and do not communicate with the PLC.
Memory tags provide an efficient means to store virtually any data value(s) in the OPC Server, and share data between OPC client applications.
Example of using a Memory Tag for Instant Messages (IM)
Creating Memory Tags
Memory tags must use the reserved keyword $MEMORY as the CPU Tagname, or File Element in the Tag Properties dialog box.
CPU Tagname $MEMORY
File Element $MEMORY
Memory tags and can be located in any Device, or Device subgroup.
Memory tags are READ/ WRITE and can be any one of the following data types:
|
OPC Canonical Type |
Type |
Range |
|
VT_BOOL |
Boolean (bit value) |
True / False |
|
VT_BOOL | VT_ARRAY |
Array of Booleans |
|
|
VT_I1 |
Signed Byte (8 bit value) |
-128 to 127 |
|
VT_I1 | VT_ARRAY |
Array of Signed Bytes |
|
|
VT_UI1 |
Unsigned Byte (8 bit value) |
0-255 |
|
VT_UI1 | VT_ARRAY |
Array of Unsigned Bytes |
|
|
VT_I2 |
Signed Short (16 bit value) |
-32786 to 32767 |
|
VT_I2 | VT_ARRAY |
Array of Signed Shorts |
|
|
VT_UI2 |
Unsigned Short (16 bit value) |
0 – 65535 |
|
VT_UI2 | VT_ARRAY |
Array of Unsigned Shorts |
|
|
VT_I4 |
Signed Long (32 bit value) |
-2147483648 to 2147483647 |
|
VT_I4 | VT_ARRAY |
Array of Signed Longs |
|
|
VT_UI4 |
Unsigned Long (32 bit value) |
0 to 4294967295 |
|
VT_I4 | VT_ARRAY |
Array of Unsigned Longs |
|
|
VT_R4 |
Float (IEEE Single Precision Real) |
1.40239846E-45 to 3.40282347E+38 |
|
VT_R4 | VT_ARRAY |
Array of Floats |
|
|
VT_BSTR |
ASCII String |
|