The Modbus lane (#741 U3) gave the driver String[] and BitInRegister[] holding-register array encoders, and
moved address resolution to ModbusTagAddressResolution (keys first, a bit region coerced to Bool, strict key
reads), but DriverArrayWriteSupport still listed both array shapes read-only (follow-up F1), so a client
write was BadNotWritable before it reached the driver.
Modbus row now mirrors the driver end to end:
- Keys shape only (region + address both present). A string-only addressString tag is resolved by the
driver with its own family through a parser Core.Abstractions cannot reference, so it stays read-only
(pinned: the conservative direction).
- Strict reads as the resolver: address an integer 0-65535; a present region / dataType / byteOrder /
stringByteOrder string must name a member.
- Coils: any dataType (coerced to Bool), <= 1968 coils (FC15).
- HoldingRegisters (FC16, never Bool): numeric, String ((stringLength+1)/2 registers, stringLength >= 1),
BitInRegister (1 register, bitIndex 0-15, span ending <= 65535), all within maxRegistersPerWrite.
FC23 is opt-in and never changes the answer.
- Elements convert (ScadaBridge int[] -> Int16 stays writable); only a String / DateTime node over a
numeric or bit element is left out, since such an element never converts.
Tests: the parity test's PendingF1 exemption and its guard are gone; the parity matrix is now region x
element type x node type against the real WriteAsync with a spec-conformant device (FC15 > 1968 refused),
plus shape edges at every cap boundary (numeric, String, BitInRegister, coil), strict key reads, FC23
on/off, string-only, the ScadaBridge int[] shape and U3 wire bytes. Core.Abstractions row tests and a
composer test (String[] and BitInRegister[] writable; over-cap, no-stringLength and string-only read-only).
Docs: table XML doc, Uns.md, modbus-addressing.md, drivers/Modbus.md, data-plane rules.
Refs #741
Claude-Session: https://claude.ai/code/session_01Ub9hGmYLQvn9XETzw7CMsT
MAJOR-1: the SDK skips TypeInfo.IsInstanceOfDataType on any node with an
OnWriteValue handler (every writable equipment node), and the node manager's
fail-fast treated numeric<->numeric as compatible, so a UInt32[] to a Galaxy
Int32 array matched MxValueEncoder's int[] arm by CLR covariance and was
written bit-reinterpreted with a Good result. EvaluateEquipmentWriteStructure
now matches an ARRAY write's element type exactly (Byte[]/ByteString the only
equivalence; Variant[]/object[] refused) -> BadTypeMismatch, nothing
dispatched. MxValueEncoder's int[]/long[] arms are exact-type guarded too, and
the Galaxy parity test's false "the SDK refuses" premise is corrected (the
UInt32/UInt64 exclusion is now the encoder's own answer). Scalar writes keep
numeric widening by decision: consumers write CLR-typed values (Double to a
Float node) and every driver's scalar encoder range-checks.
MINOR: Modbus row honours maxRegistersPerWrite (smallest of DriverConfig /
the tag's DeviceConfig, default 123) and FC15's 1968-coil ceiling, and
requires region + numeric address; Modbus/S7/Galaxy require isArray + integer
arrayLength >= 1 (Galaxy: an unbounded node would let a short write resize the
attribute); an array value to a scalar node is refused inline. Docs: Uns.md
array-write rules + upgrade note (ReadWrite array tags become client-writable
on first boot), Modbus.md, Galaxy.md.
Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe
Joseph Doherty