Reads data from Modbus devices and publishes on D-Bus. Service names and paths are per the Victron D-Bus specification.
Modbus devices using the RTU, TCP, and UDP transports are supported.
With some devices, the VregLink interface is supported.
The VregLink interface uses a block of up to 125 Modbus holding registers accessed with the Modbus Read/Write Multiple Registers function (code 23). Byte data is packed into 16-bit register values MSB first. All accesses start from offset zero in the VregLink block. The base address is device specific.
| Offset | Field |
|---|---|
| 0 | VREG ID |
| 1 | Size |
| 2..N | Data |
A write operation contains the VREG to access and, optionally, data for setting the value. The size field indicates the length in bytes of the data and must be 2x the number of registers or 1 less. To select a VREG for a subsequent read, only the first field (VREG ID) should be present.
| Offset | Field |
|---|---|
| 0 | VREG ID |
| 1 | Status |
| 2 | Size |
| 3..N | Data |
A read operation returns the value of the selected VREG or an error code if the access failed. The size field indicates the length of the data in bytes. The actual size of the VREG value is returned even if the requested number of registers is too small to contain it.
The following status codes are possible.
| Value | Meaning |
|---|---|
| 0 | Success |
| 0x8000 | Read: unknown error |
| 0x8001 | Read: VREG does not exist |
| 0x8002 | Read: VREG is write-only |
| 0x8100 | Write: unknown error |
| 0x8101 | Write: VREG does not exist |
| 0x8102 | Write: VREG is read-only |
| 0x8104 | Write: data invalid for VREG |
If the VregLink register block begins at address 0x4000, then to read VREG 0x100 (product ID), the following Modbus transaction would be used.
| Field Name | Hex | Comment |
|---|---|---|
| Request | ||
| Function | 17 | Read/Write Multiple Registers |
| Read Starting Address Hi | 40 | VregLink base address |
| Read Starting Address Lo | 00 | |
| Quantity to Read Hi | 00 | |
| Quantity to Read Lo | 05 | |
| Write Starting Address Hi | 40 | VregLink base address |
| Write Starting address Lo | 00 | |
| Quantity to Write Hi | 00 | |
| Quantity to Write Lo | 01 | |
| Write Byte Count | 02 | |
| Write Register Hi | 01 | PRODUCT_ID |
| Write Register Lo | 00 | |
| Response | ||
| Function | 17 | Read/Write Multiple Registers |
| Byte Count | 0A | |
| Read Register Hi | 01 | PRODUCT_ID |
| Read Register Lo | 00 | |
| Read Register Hi | 00 | Status: success |
| Read Register Lo | 00 | |
| Read Register Hi | 00 | Size: 4 |
| Read Register Lo | 04 | |
| Read Register Hi | 00 | Product ID |
| Read Register Lo | 12 | |
| Read Register Hi | 34 | |
| Read Register Lo | FE |
To set VREG 0x10C (description), the Modbus transaction might look as follows.
| Field Name | Hex | Comment |
|---|---|---|
| Request | ||
| Function | 17 | Read/Write Multiple Registers |
| Read Starting Address Hi | 40 | VregLink base address |
| Read Starting Address Lo | 00 | |
| Quantity to Read Hi | 00 | |
| Quantity to Read Lo | 02 | |
| Write Starting Address Hi | 40 | VregLink base address |
| Write Starting address Lo | 00 | |
| Quantity to Write Hi | 00 | |
| Quantity to Write Lo | 08 | |
| Write Byte Count | 10 | |
| Write Register Hi | 01 | DESCRIPTION1 |
| Write Register Lo | 0C | |
| Write Register Hi | 00 | Size: 11 |
| Write Register Lo | 0B | |
| Write Register Hi | 4D | 'M' |
| Write Register Lo | 79 | 'y' |
| Write Register Hi | 20 | ' ' |
| Write Register Lo | 50 | 'P' |
| Write Register Hi | 72 | 'r' |
| Write Register Lo | 65 | 'e' |
| Write Register Hi | 63 | 'c' |
| Write Register Lo | 69 | 'i' |
| Write Register Hi | 6f | 'o' |
| Write Register Lo | 75 | 'u' |
| Write Register Hi | 73 | 's' |
| Write Register Lo | 00 | Padding |
| Response | ||
| Function | 17 | Read/Write Multiple Registers |
| Byte Count | 04 | |
| Read Register Hi | 01 | DESCRIPTION1 |
| Read Register Lo | 0C | |
| Read Register Hi | 00 | Status: success |
| Read Register Lo | 00 |