Modbus register address, in decimal form. Note that Modbus documentation is not consistent, and it may be necessary to modify the address. 

For example, many addresses are listed with a preceding 3 or 4, but this number is usually dropped along with any preceding 0s. Thus, 30001 becomes 1, 40258 becomes 258, and so on. Some addresses may have a +/- 1 offset, so 301 might actually need to be entered as 300. Finally convert hex values (which usually start with 0x) to decimal values using a hexidecimal to decimal converter.

The register name is an arbitrary value, but should reflect the item being measured for the sake of clarity. For example, "Temperature" implies a temperature measurement. "Ambient Temperature" might be a better fit for a device which records multiple temperature measurements.

The data type of the register. If this setting is not correct the register data will not be read correctly, although it will usually read something. 32 and 64 bit data types read more than one Modbus register (a single Modbus register is 16 bits). In the absence of a defined data type, a register described by an address range (eg, 10-11, or 1000-1003) is likely a 32 or 64 bit register.

16 bit value options:  (AB) (BA)

32 bit value options:  (AB CD) (CD AB) (BA DC) (DC BA) or a custom option where the order can be specified.

64 bit value options: (AB CD EF GH) (GH EF CD AB) (BA DC FE HG) (HG FE DC BA) or a custom option where the order is specified.

Introduced in Firmware v4.7

This setting allows the user to define a specific byte order.  eGauge default is to read values is big-endian byte order, or little-endian for data types ending with ‘l’ (for example: s32 data type is read as big-endian and s32l would be interpreted as litte-endian) 

Setting the byte-order setting to ‘custom’ or one of the other pre-defined byte orders allows for additional options beyond the default settings.  The correct byte-order to use may need to be confirmed with the hardware manufacturer.

The kind of register. There are three options:

• Analog - A simple numerical value. Most applications will use analog values.
• Bitset - A numerical value representing a binary string. Typically, each 1 or 0 in this string would represent a state on the remote device. This selection is never averaged or allowed to accumulate excess, because it would change the fundamental value.
• Enum - A numerical value representing a state on the remote device. This selection is never averaged or allowed to accumulate excess, because it would change the fundamental value.

Applies a scale factor to the raw value read from the Modbus device. This may be used to scale incoming values to better fit a certain data type. In the example above, the Temperature register at address 1 records temperature in .1 C increments, but the eGauge uses C as a unit. A raw value of 334 would therefore be displayed and recorded as 33.4 degrees Celsius with a .1 scale factor. If left blank, this is set to "1".

Applies a numerical offset to a raw value. This may be used for calibration purposes (eg, if a sensor is known to read 2 units too low, an offset of 2 would display the reading from that sensor as "raw_value + 2"). If left blank, this is set to "0".

Associates a supported unit with the value recorded from that register. This assigns a unit to the register in the eGauge user interface. For unsupported units, "record as integer" will record whole numbers and "record with 3 digits" will record fractional numbers to three digits (note that the incoming data may not actually be precise to three digits). 

The eGauge supports reading values from remote devices using either function code 3 (read holding registers) or function code 4 (read input registers). By default, function code 3 is used. However, some devices may only support function code 4 - in this case, selecting "read-only input register" will force the eGauge to use function code 4 for that register. Note that it is possible to use a mix of function codes on a single device.

The default unit number is also referred to as "Modbus ID", "Modbus slave address", "Slave address", and so on. Each device on a single serial chain must have a unique unit number. Typically, hardware will ship with a default unit number, so if multiple devices from the same manufacturer are preset the unit number must be set to a unique value on each device.

Most Modbus RTU devices ship with a predefined set of serial parameters. These include baud rate, data bits, parity, and stop bits. These parameters must be identical across all devices on a single serial chain. If using multiple identical devices they should all be set to use the same values, but devices from different manufacturers may need to be set so they all use the same serial parameters.

Most Modbus TCP devices ship with a default TCP port of 502. However, in some cases this may not be true, or it may be desirable to use a different TCP port. TCP ports do not need to match across multiple Modbus TCP devices, even on the same network (each Modbus TCP device should have a unique IP address, so the port used is immaterial).

The base address field can be used to apply a starting address for registers. This can be useful if a manufacturer's Modbus map has a +/-1 offset, or if the addresses all require a specific prefix (eg, 30000, 40000, 1000). The address queried by the eGauge will be (base address) + (configured address).