ModSnmp Manual v3.10 - 6.3.1. SNMP settings
SNMP Name. Enter a name for the object. This will be used to generate the object descriptor in the MIB file. It must start with a capital letter, contain only letters and digits, and be at most 18 characters long. The name "Description" is reserved for the device description.
SNMP Description. Optionally enter a description of the object. This will be used as the object description in the MIB file. It may contain only displayable ASCII characters (including spaces, tabs, and newlines), and must not contain double quote (").
SNMP Number. Enter the number of variables (SNMP instances) in the group. For a scalar object, enter 1. The number should not exceed the number of variables actually supported by the Modbus device: SNMP managers often "walk" through tables, and this will generate Modbus errors if the number is too large.
ModSnmp supports the following SNMP types (see RFC 2578 for fuller descriptions):
Table 2. SNMP types
SNMP type Description Integer32 An Integer32 is a signed 32-bit integer (i.e. in the range -2147483648 to 2147483647 decimal). The INTEGER type used in SNMPv1 is identical to Integer32. Unsigned32 An Unsigned32 is an unsigned 32-bit integer (i.e. in the range 0 to 4294967295 decimal). Gauge32 A Gauge32 is also an unsigned 32-bit integer (i.e. in the range 0 to 4294967295 decimal). Counter32 A Counter32 is an unsigned 32-bit integer (i.e. in the range 0 to 4294967295 decimal) that monotonically increases until it reaches a maximum value of 4294967295, when it wraps around and starts increasing again from zero. A Counter32 is read-only. TimeTicks A TimeTicks is an unsigned 32-bit integer (i.e. in the range 0 to 4294967295 decimal) that represents a time interval in hundredths of a second. Counter64 A Counter64 is an unsigned 64-bit integer (i.e. in the range 0 to 18446744073709551615 decimal) that monotonically increases until it reaches a maximum value of 18446744073709551615, when it wraps around and starts increasing again from zero. A Counter64 is read-only. OctetString An OctetString is arbitrary binary or textual data. If you select OctetString, the Modbus value will be sent in the SNMP response as a sequence of bytes, most significant byte first. Float This is not a genuine SNMP type. It is provided by ModSnmp as a means of transporting floating-point values via SNMP (SNMP does not currently have a floating-point type). If you select Float, ModSnmp will interpret the Modbus value as floating-point, convert it to a UTF-8 text string, and return it to the SNMP manager as an OctetString. BITS This is an OctetString with names for the individual bits of the value.
SNMP does not have 16-bit types, so you will normally have to select one of the 32-bit types for transferring values of 16-bit Holding or Input registers.
You can use any type except Float for transferring Coils and Discrete Inputs. You should set the Modbus Size to the number of Coils or Discrete Inputs that you want to transfer in each SNMP instance.
SNMP Bit Names. If you selected the SNMP BITS type, you must enter a name for each bit of the value. Names may contain only letters and digits and must start with a lower-case letter. Each name may contain at most 64 characters.