DIGITAL SIGNATURE (VALID ONLY FOR WM3M4C)
User’s Manual WM3M4 &WM3M4C
Signature process starts after every command. Control unit can read out signed dataset with current
time and energy meter value reading.
Meter stores one value (timestamp and counter value) for each command. Registers are defined in
measurements table (0).
If ‘r’ command is sent, array with begin and end reading is generated and signed.
Hold command is used for read and sign later procedure. Every energy value reading is stored by
default. When ‘h’ command is sent, stored value is used for next signature instead of actual energy
counter value.
6.5.9 Signature status
Control unit must check signature status before reading signed dataset and signature. Signing process
takes up to 1 second, so control unit must check status few times with some delay.
MODBUS register address is 47052. Signature OK value is 15.
6.5.10 Output billing dataset
Signature process modifies original billing dataset, which was entered at start of measuring. Output
billing dataset contains meter information (meter vendor, meter model, meter serial number and
firmware version), measured value and unique pagination value (PG). Output billing dataset is
available until next signature request or power down.
JSON and binary output are supported.
Only 120 MODBUS registers (240 bytes) can be read in one MODBUS read command.
6.5.11 JSON output
Size of JSON output billing dataset is at MODBUS address 47057.
JSON output billing dataset is at MODBUS address 47612.
6.5.12 Binary output
Size of binary output billing dataset is at MODBUS address 48316.
Binary output billing dataset is at MODBUS address 48317.
6.5.13 Signature
After successful signature process, control unit can read signature in specified signature format.
Signature length register is at MODBUS address 47058.
Signature register is at 48188.
6.5.14 Public key
Public key is stored in 64 bytes raw format at MODBUS address 48124.
For Transparenz Software check, public key header should be prepended:
3059301306072A8648CE3D020106082A8648CE3D03010703420004
For checking with ECDSA, public key header is: 04.
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