The DL205 family-native branch routed every V-prefixed address through
DirectLogicAddress.UserVMemoryToPdu, a plain octal-to-decimal decode.
DL205/DL260 system V-memory (V40400 and up) is not a simple octal decode:
the CPU relocates the system bank to Modbus PDU 0x2100. Octal-decoding
V40400 produced 16640 (0x4100), the wrong register, so any tag addressing
a system register through the grammar string silently read/wrote the
wrong PLC memory.
- Add DirectLogicAddress.VMemoryToPdu, which decodes the octal V-address,
detects the system bank (octal >= V40400 == SystemVMemoryOctalBase) and
relocates it through SystemVMemoryToPdu to PDU 0x2100; user-bank
addresses keep the plain octal decode.
- ModbusAddressParser's DL205 V branch now calls VMemoryToPdu instead of
UserVMemoryToPdu. UserVMemoryToPdu is retained for user-bank-only callers.
- Correct the ModbusFamilyParserTests V40400 assertion (16640 -> 0x2100)
and add system-bank regression cases plus direct helper coverage.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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