Configuration

Connection Options

public sealed class ModbusClientOptions
{
    // Either Host or IpAddress must be provided
    public string? Host { get; init; }
    public IPAddress? IpAddress { get; set; }
    
    // Defaults to 502 (standard Modbus TCP port)
    public int? Port { get; set; } = 502;
    
    // Register byte/word ordering (see Register Packing section)
    public RegisterPacking Packing { get; set; } = RegisterPacking.WordHighFirstByteBigEndian;
}

Host vs IpAddress

• Use Host for DNS-based resolution (supports dynamic IPs, retries DNS on reconnect)
• Use IpAddress for direct IP connection (slightly faster, no DNS overhead)
• If both are set, Host takes precedence

Port

• Standard Modbus TCP uses port 502
• Custom ports logged at startup for troubleshooting

Register Packing

Multi-register values (32-bit floats, 64-bit integers) require configuring how bytes/words are ordered. This varies by manufacturer:

public enum RegisterPacking
{
    // Most common (Eastron SDM, Schneider, Carlo Gavazzi, SMA, Fronius)
    WordHighFirstByteBigEndian,  // ABCD
    
    // Word-swapped (some PLCs, older devices)
    WordLowFirstByteBigEndian,   // CDAB
    
    // Rare variants
    WordHighFirstByteLittleEndian,  // BADC
    WordLowFirstByteLittleEndian    // DCBA
}

Troubleshooting Register Packing

• If values are wildly incorrect (e.g., active power = 1.23E-38), try WordLowFirstByteBigEndian
• Consult device manual for "float byte order" or "register format"
• Test with known values (e.g., read voltage when actual voltage is known)

Common Device Formats

Device/Manufacturer	Typical Packing
Eastron SDM series	WordHighFirstByteBigEndian (ABCD)
Schneider Electric	WordHighFirstByteBigEndian (ABCD)
Carlo Gavazzi	WordHighFirstByteBigEndian (ABCD)
SMA inverters	WordHighFirstByteBigEndian (ABCD)
Fronius inverters	WordHighFirstByteBigEndian (ABCD)
Some older PLCs	WordLowFirstByteBigEndian (CDAB)

TIP

Most modern energy meters and inverters use WordHighFirstByteBigEndian (ABCD format), which is the default.

WARNING

If you see values like 1.23E-38 or NaN when reading floats, your register packing is likely incorrect. Try switching between WordHighFirstByteBigEndian and WordLowFirstByteBigEndian.