WattNode Modbus Option Identification

There are cases where you may have purchased a WattNode^® Modbus^® meter with options and need to determine which options are present. There are a few approaches.

• The front label shows the options in the central gray rectangle below the model number.
• Your shipping list and invoice should show the options.
• You can read the option information registers.
• You can read the Options register.
• You can contact Continental Control Systems for the information.

Once you have determined which options are present, see WattNode Modbus – Options or the manual for details.

Reading the Option Information Registers

For all of the following option information registers, a value of zero (0) indicates that the option isn’t present or installed. Unless otherwise specified, a value of one (1) indicates that the option is present. This can be easier to interpret compared to reading the Options register (described in the next section).

The option information registers were added for WattNode Modbus meter firmware version 16. For older versions, see Reading the Option Register below.

Reading the Options Register

Before firmware version 16, this was the only way to determine installed options, but there is now another way by reading the option information registers (see above). However, the Options register also shows additional factory configured settings for certain features that are based on the firmware version and/or the specific meter model, rather than being based on a special order option.

The Options register is located at location 1709 and indicates factory configured options. The Options register can only be set at the factory, but many of the settings applied by options can also be field configured using the communication registers (Address, Baud, ParityMode, etc.).

The table below shows how to interpret the value read back from the Options register:

Note 1: The CT amps can only be reconfigured for non-revenue models.

Note 2: “Option IO” is a hardware option, but it’s behavior as an input or output is user configurable.

Note 3: WattNode Revenue for Modbus models are always factory programmed with bits 10 and 11 set, to specify the CtAmps and lock the settings. See Why Are Some Settings Locked on Revenue Meters? for details.

For each option that applies there is a bit (or binary digit) set in the Options register. When only a single option applies, the register value represents the decimal weight for that bit. If multiple options are selected, then the bit values add together. For example, if you order Option 38K (bit 2 set = 4 decimal or 100 binary) with Option TTL (bit 4 set = 16 decimal or 10000 binary), the Options register will read back a value of 20 decimal (both bits 2 and 4 set = 14 hexadecimal or 10100 binary).

Where the meter has many options, it is easiest to determine which options apply by converting the Options register value from a decimal integer into a binary number. The binary number format indicates each option as a separate bit which is represented as either a “1” (one bit, which indicates the option is present) or a “0” (zero bit). Calculators for doing this conversion are available on the web (for example, see http://www.binaryhexconverter.com/decimal-to-binary-converter). Alternatively, the Calculator accessory in the Windows OS is a standard program that has a special View that can do decimal-to-binary conversions. To use it for these conversions you can launch it from the Windows Accessory group and click on the Calculator’s View menu item. Then click on the “Programmer” selection. In a binary number, the bit positions are “zero-based”. That means that the least significant bit (or the bit furthest to the right) is called “bit 0”, the next most significant bit (or next bit over from the right-most) is “bit 1” and so on.

Some options such as the communication options (TCP-RTU, EP, 19K, AD, and 38K) can be overridden in the field by writing to the communication registers. If you wish to revert to the factory configured options, set all the DIP switches to the OFF position for ten seconds to restore all communication configuration registers to their factory defaults—including any selected options. See the appropriate meter manual for more details on which options are user configurable and how to change them.

Examples for Identifying a Revenue Grade Meter

Example Using the Options Register (1709)

When this register is read from a revenue grade meter, bit 10 and/or bit 11 is set so you would mask off all other bits and test for a non-zero result. Reading the Options register returns a normal data response from any meter regardless of how old its firmware is.

Example Using the Report Slave ID Command

When the Report Slave ID (Modbus function code 17) command is issued, a revenue grade meter response contains a string such as, “Continental Control Systems LLC, WattNode MODBUS, RWNC-3Y-208-MB”, where the model prefix is “RWNC” instead of “WNC”.

Example using the OptRevenueGrade Register (1737)

When this register is read and it’s a revenue-grade meter, a value of one is returned; otherwise, a zero value indicates it’s a non-revenue model. However, this register does not exist in meters manufactured before 3/15/2015 (when V22 firmware was released), which will therefore reply with an Illegal Register Address exception response (Modbus exception code 2). For meters with firmware that predates V22, use one of the methods above instead to determine if it’s revenue grade.

See Also

• WattNode Modbus – Options
• WattNode Modbus Firmware Versions