Mastervolt MasterBus-Modbus interface
Register map(s) for this device, with a note of how far each has been checked. Addresses are
0-based, as on the wire. Scale and byte order are confirmed only at the hardware-verified rung.
coherence-checked
Round-trips through a real Modbus stack with no overlapping addresses and a word-order-sensitive codec — the map is internally coherent and wire-decodable. Does NOT prove byte-order or scaling match a real device: the emulator is seeded from the map's own types, so a uniformly wrong byte-order still round-trips. Only hardware-verified confirms byte-order/scale on the wire.
| point | address (0-based) | type | scale | unit |
|---|
| idal_idb_hi | 0 | U16 | 1 | |
| idb_lo | 1 | U16 | 1 | |
| tab_nr | 2 | U16 | 1 | |
| index | 3 | U16 | 1 | |
| value | 4 | F32LE | 1 | |
link settings as documented (unverified): RTU; default 19200 8E?; unit ID 1; FC 23; Uses Modbus function 23 (0x17) Read/Write Multiple Registers Protocol to bridge to MasterBus.
bench facts as documented (unverified)
| terminals | Screw terminal |
| A/B polarity | B line, A line, Ground |
| termination | MasterBus Terminating device included |
| connector | Screw terminal |
| wiring notes | Din rail mounting: Yes, Din rail 30 mm [1.2 inch] |
| max registers/read | 6 |
| response timeout | 3000 ms |
| protocol notes | Only supports Modbus function code 23 (0x17). Read Starting Address must be 0, Quantity to Read must be 6, Quantity to Write must be 6. |
| power | 350 mW |
| environment | Protection degree: IP 21 |
| certifications | CE, 2004/108/EC (EMC directive), 2011/65/EU (RoHS directive) |
| doc revision | v 1.4 September 2014 |
⚠ disputed: Polarity: B line, A line, Ground — disputed by the March 2009 manual version (v1.0) which states '1. Modbus A line, 2. Modbus B line, 3. Modbus Ground' [1.1.2], whereas the September 2014 manual version (v1.4) and physical terminal labels state '1. Modbus B line, 2. Modbus A line, 3. Modbus Ground'.
field reports — community-sourced, unverified (checked 2026-06-11)
- The MasterBus Modbus Interface uses a highly non-standard Modbus implementation relying exclusively on Function Code 23 (0x17) Read/Write Multiple Registers, making it incompatible out-of-the-box with many standard Modbus drivers and controllers (such as Victron Cerbo GX or standard PLCs) without custom scripting. [source]
- Integrating the MasterBus Modbus Interface with home automation systems (like Jeedom or Node-RED) requires custom scripting or specialized plugins (e.g., plugin-mymodbus) to handle the non-standard Function Code 23 (0x17) polling and action commands. [source]
- confirmed: Uses Modbus function 23 (0x17) Read/Write Multiple Registers Protocol to bridge to MasterBus. — confirmed by the MasterBus Modbus Interface User Manual (September 2014) which details the exclusive use of Function Code 23 (0x17) for reading and writing variables [1.2.3].
- confirmed: Read Starting Address must be 0, Quantity to Read must be 6, Quantity to Write must be 6. — confirmed by the MasterBus Modbus Interface User Manual under the Modbus Exception Codes section (Exception Codes 02 and 03).
- confirmed: Baud rates [9600, 19200, 115200] with default 19200, default unit ID 1, and Even parity. — confirmed by the configuration specifications in the MasterBus Modbus Interface User Manual.
- confirmed: Protection degree: IP 21, power consumption 350 mW, and DIN rail mounting. — confirmed by the physical specifications in the MasterBus Modbus Interface User Manual.
The trust ladder
Each rung states what it proved and what it did not. Gray until proven; green is earned by hardware only.
- generated — A prompt produced it. Unproven — anyone can regenerate this.
- structure-verified — Decode path is structurally sound (addresses, widths, finite values). Does NOT prove word order or scaling.
- coherence-checked — Round-trips through a real Modbus stack with no overlapping addresses and a word-order-sensitive codec — the map is internally coherent and wire-decodable. Does NOT prove byte-order or scaling match a real device: the emulator is seeded from the map's own types, so a uniformly wrong byte-order still round-trips. Only hardware-verified confirms byte-order/scale on the wire.
- hardware-verified (software-key) x1 — Matched a real device with operator-attested readings as ground truth — the only rung that confirms word order + scaling on the wire.