# MUST PV1800 register map

Derived from the manufacturer protocol document
`PH1800 PV1800 EP1800 PV3500 EP3500 RS485 Modbus RTU communication Protocol 1.4.15.xlsx`
shipped in the [taHC81/MUST-ESPhome](https://github.com/taHC81/MUST-ESPhome)
GitHub repo. Only the registers this monitor reads are listed here;
the full document covers hundreds more.

All values are Modbus RTU holding registers (function code 0x03),
unless otherwise noted. RO = read-only, RW = read/write.

## CHARGER block (start at 15201)

| Addr | RO/RW | Name | Unit | Notes |
|------|-------|------|------|-------|
| 15201 | RO | Charger workstate | — | 0=Init, 1=Standby, 2=Charging, 3=Fault, 4=Flash |
| 15202 | RO | MPPT state | — | 0=Stop, 1=Start, 2=Normal, 3=MPPT limit, 4=Float |
| 15203 | RO | Charging state | — | 0=Stop, 1=Precharge, 2=CC, 3=CV, 4=Float, 5=Current derating |
| 15204 | RO | reserved | — | |
| 15205 | RO | PV voltage | 0.1 V | |
| 15206 | RO | Battery voltage (charger side) | 0.1 V | |
| 15207 | RO | Charger current | 0.1 A | |
| 15208 | RO | Charger power | W | |

When you ask for register 15201 with `count=1` the inverter dumps the
entire block (49 registers, addresses 15201..15249). The registers
listed here are 15201..15208.

## INVERTER block (start at 25201)

| Addr | RO/RW | Name | Unit | Notes |
|------|-------|------|------|-------|
| 25201 | RO | Work state | — | 0=PowerOn, 1=SelfTest, 2=OffGrid, 3=GridTie, 4=ByPass, 5=Stop, 6=GridCharging |
| 25202 | RO | AC voltage grade | V | 230=230V variant, 120=120V variant |
| 25203 | RO | Rated power | VA | |
| 25204 | RO | reserved | | |
| 25205 | RO | Battery voltage | 0.1 V | |
| 25206 | RO | Inverter voltage | 0.1 V | |
| 25207 | RO | Grid voltage | 0.1 V | |
| 25208 | RO | BUS voltage | 0.1 V | |
| 25209 | RO | Control current | 0.1 A | |
| 25210 | RO | Inverter current | 0.1 A | |
| 25211 | RO | Grid current | 0.1 A | |
| 25212 | RO | Load current | 0.1 A | |
| 25213 | RO | PInverter | W | **signed** in this script; protocol says unsigned 1W |
| 25214 | RO | PGrid | W | signed (negative = exporting to grid) |
| 25215 | RO | PLoad | W | signed (negative = ??? on this firmware) |
| 25216 | RO | Load percent | % | unit is percent (raw integer, NOT ×0.01) |
| 25217 | RO | SInverter | VA | |
| ... | | (more S/Q regs, frequencies, temps, relays, accumulators) | | |
| 25233 | RO | AC radiator temperature | °C | |
| 25234 | RO | Transformer temperature | °C | |
| 25235 | RO | DC radiator temperature | °C | often 0 on units without that sensor |
| ... | | | | |
| 25273 | RO | Batt power | W | signed |
| 25274 | RO | Batt current | 0.1 A | signed |
| 25275 | RO | Batt voltage grade | V | 12, 24, or 48 |

This monitor polls 25201..25274 (74 registers). The inverter returns
all of them in one response when asked.

## SETTINGS blocks (split into two ranges)

### 10103..10104

| Addr | RO/RW | Name | Unit |
|------|-------|------|------|
| 10103 | RW | Float voltage | 0.1 V |
| 10104 | RW | Absorb voltage | 0.1 V |

### 20118..20132

| Addr | RO/RW | Name | Unit |
|------|-------|------|------|
| 20118 | RW | Battery stop discharging voltage | 0.1 V |
| 20119 | RW | Battery stop charging voltage | 0.1 V |
| 20127 | RW | Battery low voltage | 0.1 V |
| 20128 | RW | Battery high voltage | 0.1 V |
| 20132 | RW | Max combine charger current | 0.1 A |

## Decoded state values

These are the canonical values from protocol v1.4.15, verified by
cross-checking the XLSX shipped with the
[taHC81/MUST-ESPhome](https://github.com/taHC81/MUST-ESPhome) repo
against the same document uploaded to
[Scribd](https://www.scribd.com/document/881604771/) (document 881604771).

### Charger workstate (15201)

| Value | Meaning |
|-------|---------|
| 0 | Initialization mode |
| 1 | SelfTest mode |
| 2 | Work mode |
| 3 | Stop mode |

### MPPT state (15202)

| Value | Meaning |
|-------|---------|
| 0 | Stop |
| 1 | MPPT |
| 2 | Current limiting |

### Charging state (15203)

| Value | Meaning |
|-------|---------|
| 0 | Stop |
| 1 | Absorb charge |
| 2 | Float charge |
| 3 | EQ charge (equalization) |

### Inverter workstate (25201)

| Value | Meaning |
|-------|---------|
| 0 | PowerOn |
| 1 | SelfTest |
| 2 | OffGrid |
| 3 | Grid-Tie |
| 4 | ByPass |
| 5 | Stop |
| 6 | GridCharging |

> **Note:** Earlier versions of this file and the monitor script had
> incorrect values for 15201–15203. They were originally derived from
> a misreading of the protocol document. If you ran the script before
> the 2026-09-10 fix, you may have seen "Standby", "Charging",
> "Float" etc. where the correct values are "SelfTest mode", "Work
> mode", "Float charge". The protocol doc and the live readings agree;
> the old decode tables did not.

## Notes on this unit

- Battery voltage grade is 24 V (24V battery system).
- AC voltage grade is 120 V (120V variant, not the 230V default).
- Confirmed against live readings: `Battery voltage = 28.2 V`,
  `Inverter voltage = 115.7 V`, `Grid voltage = 117.0 V`.