Data Types
- Last UpdatedDec 17, 2021
- 3 minute read
All managed objects defined under SNMP are based on the three ASN.1 UNIVERSAL types:
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INTEGER - A signed whole number with no specific size limit, although most SNMP implementations define INTEGERs to be signed or unsigned 32-bit numbers.
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OCTET STRING - A sequence of octets, where each octet is defined as an 8-bit byte. The sequence may be printable ASCII characters or arbitrary binary data.
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OBJECT IDENTIFIER - Stores the location of a variable (managed object) within an MIB. The location is stored as an array of 16-bit unsigned integers called sub-identifiers.
The following table describes the data types, address format, Plant SCADA data type, and applicable SNMP data type.
|
Data Types |
Address Format |
Plant SCADA Data Type |
Applicable SNMP Data Type |
|
Alphanumeric (display string) objects |
DAn |
STRING |
ASN_OCTETSTRING, ASN_BITS, ASN_OPAQUE, ASN_IPADDRESS, ASN_OBJECTIDENTIFIER |
|
Alphanumeric (binary string) objects |
BAn |
STRING |
ASN_OCTETSTRING, ASN_BITS, ASN_OPAQUE |
|
Numeric objects (treat as long in Plant SCADA ) |
Nn |
LONG |
ASN_INTEGER, ASN_INTEGER32, ASN_UNSIGNED32, ASN_COUNTER64, ASN_COUNTER32, ASN_GAUGE32, ASN_TIMECLIDKS |
|
Numeric objects (treat as real in Plant SCADA ) |
Rn |
REAL |
ASN_INTEGER, ASN_INTEGER32, ASN_UNSIGNED32, ASN_COUNTER64, ASN_COUNTER32, ASN_GAUGE32, ASN_TIMECLIDKS |
|
Trap objects (null terminated string) |
Ta |
STRING |
Trap object |
|
Trap objects (binary string) |
BTa |
STRING |
Trap object (only for ASN_OCTETSTRING, ASN_BITS, ASN_OPAQUE type value in varbinding field). |
|
Trap forwarding (write only) |
TF |
STRING |
IP address to forward a copy of the last trap to. One IP address is required per call to TF. TF can be called multiple times. |
|
Trap Next (read and write) |
TN |
LONG |
TN as read is the traps in queue, 0 for nothing. A TN write removes the current entry and gets the next. |
|
Multiple Trap Variable |
TNVB |
LONG |
A read of TNVB returns the number of varbinds in the trap, a write to TNVB controls which varbinds data is read or written to. |
Where:
|
n |
0 to 65535 |
|
a |
0 to 6 (T0 to T6 are read and write variables) |
For string types, DA stands for null-terminated string and BA for binary string.
A null-terminated string is a string with 0x00 as an end flag, but in a binary string a 0x00 may be valid content.
For example, <0x41><0x42><0x43><0x00><0x61><0x62><0x63>:
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If defined as DA, Plant SCADA will display it as 'ABC' and the content from <0x61> will be truncated.
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If defined as BA, Plant SCADA will display it as '41424300616263'.
This also applies to those ASN_OCTETSTRING type fields in a trap object, with DA replaced by T, and BA replaced by BT.
Whether a tag is readable/writable depends on how the SNMP object to which it corresponds is defined in the appropriate .MIB file.
For the type DA, BA, N and R, the n represents the value of the INDEX field for a tag's entry in the SNMPVARS.DBF file.
You should not directly modify the tag database.
For each tag, you can specify the Plant SCADA data type you require; however you have to verify that the selection you make is appropriate for the corresponding SNMP object.
Tags with a Plant SCADA data type of STRING are limited to a maximum length of 255 characters. Tags with a required numeric range outside the range 147483648 to 2147483647 can be assigned a Plant SCADA data type of REAL.