| Address range | **Description** |
| **Timestamps** | |
| 30000 -- 30003 | local timestamp (for use when reading from addresses <35000) |
| 30004 -- 30007 | THD timestamp indicates when data was acquired that is used by FFTarg(), FFTarg2(), FFTmag(), and THD() functions |
| 30008 -- 30009 | register timestamp (for use when reading from addresses ≥35000) |
| **Local data (channel checker)** | |
| 30500 -- 30999 | Line voltages (RMS) |
| 31000 -- 31499 | Line voltages (DC/mean) |
| 31500 -- 31999 | Line frequencies |
| 32000 -- 32499 | Sensor values (normal/RMS) |
| 32500 -- 32999 | Sensor values (mean/DC) |
| 33000 -- 33949 | Sensor frequencies |
| **Register Data \[v4.0 and greater\]** | |
| 34000 -- 34999 | Reduced precision cumulative physical register values (float) |
| 35000 -- 35999 | Cumulative virtual register values (signed 64-bit integers) |
| 36000 -- 36999 | Change of virtual register value (float) |
| 37000 -- 37999 | Reduced precision cumulative virtual register values (float) |
| 38000 -- 38999 | Cumulative physical register values (signed 64-bit integers) |
| 39000 -- 39999 | Change of physical register value (float) |
| **Register Data \[PRIOR to firmware v4.0, now deprecated\]** | |
|---|---|
| 35000 -- 35999 | Cumulative register values (signed 64-bit integers) \[DEPRECATED\] |
| 36000 -- 36999 | Change of register value (float) \[DEPRECATED\] |
| 37000 -- 37999 | Reduced precision cumulative register values (float) \[DEPRECATED\] |
The t16 type Modbus registers are variable-length UTF-8 strings and therefore multiple registers may need to be read until a UTF-8 null character is reached.
# Example Modbus Transmissions: ## Example Modbus TCP request and response for L1 RMS voltage: ### Request: \[00 01\] \[00 00\] \[00 06\] \[01\] \[04\] \[01 f4\] \[00 02\] \[00 01\] = Transaction identifier \[00 00\] = Protocol identifier (always 00 00) \[00 06\] = Bytes following (0x0006 = 6 bytes) \[01\] = Unit ID \[04\] = Function code (0x04 is read input registers) \[01 f4\] = Starting register address (500) \[00 02\] = Number of words to return (2 words for float value) ### Response: \[00 01\] \[00 00\] \[00 07\] \[01\] \[04\] \[04\] \[42 f6 2a 06\] ### \[00 01\] = Transaction identifier \[00 00\] = Protocol identifier (always 00 00) \[00 07\] = Bytes following (0x0007 = 7 bytes) \[01\] = Unit ID \[04\] = Function code (0x04 is read input registers) \[42 f6 2a 06\] = Contents of register 500 and 501 respectively 0x42f62a06 decoded as big-endian (ABCD) float is roughly 123.08, so L1 voltage is 123.08Vrms ## Example Modbus RTU request and response for L1 RMS voltage: ### Request: \[01\] \[04\] \[01 f4\] \[00 02\] \[31 c5\] \[01\] = Unit ID \[04\] = Function code (0x04 is read input registers) \[01 f4\] = Starting register address (500) \[31 c5\] = CRC error check ### Response: \[01\] \[04\] \[04\] \[42 f6 2a 06\] \[90 ac\] \[01\] = Unit ID \[04\] = Function code (0x04 is read input registers) \[04\] = Data bytes to follow (not including CRC) \[42 f6 2a 06\] = Contents of register 500 and 501 respectively 0x42f62a06 decoded as big-endian (ABCD) float is roughly 123.08, so L1 voltage is 123.08Vrms --- # Additional technical informationThe maximum Modbus frame size is 255 bytes. This translates to (61) 32-bit registers or (30) 64-bit registers. Most DAS and Modbus systems will automatically split any requests to limit the response size to not exceed the upper limit. If requesting more registers than can be returned in a single frame, the response may be truncated or an exception may be returned.
Additional help is available by clicking the \[?\] buttons on the Modbus Server settings page. All data is provided as Modbus input registers and therefore their Modbus addresses start at 30000. The raw frame sent does not include the prefixed '30', this indicates the function code used. For each register recorded by eGauge, the register's current cumulative value and the amount by which it changed since the previous one-second interval can be read. The cumulative value is available with full resolution as a signed 64-bit value. For convenience, the same value is also available, at reduced resolution, as a 32-bit floating point number. The change-in-value is available only as a 32-bit floating point number. In addition to the register data, it is also possible to read locally measured data such as line-voltages, frequencies, and the value measured by each sensor-port. The Modbus server guarantees that any data read with a single request is consistent. Timestamps are provided as a means to ensure consistency when data is read with multiple requests (e.g., to read multiple, discontiguous registers). This is accomplished by (i) reading the timestamp, (ii) performing the desired read requests, and (iii) reading the timestamp again. If the two timestamp values are the same, then reader can be certain that the data is consistent.