diff --git a/src/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/AbLegacyDataType.cs b/src/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/AbLegacyDataType.cs
index 48e253d..fc55970 100644
--- a/src/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/AbLegacyDataType.cs
+++ b/src/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/AbLegacyDataType.cs
@@ -109,4 +109,103 @@ public static class AbLegacyDataTypeExtensions
         AbLegacyDataType.MicroLogixFunctionFile => DriverDataType.Int32,
         _ => DriverDataType.Int32,
     };
+
+    /// <summary>
+    ///     Sub-element-aware driver type. Timer/Counter/Control elements expose Boolean status
+    ///     bits (<c>.DN</c>, <c>.EN</c>, <c>.TT</c>, <c>.CU</c>, <c>.CD</c>, <c>.OV</c>,
+    ///     <c>.UN</c>, <c>.ER</c>, etc.) and Int32 word members (<c>.PRE</c>, <c>.ACC</c>,
+    ///     <c>.LEN</c>, <c>.POS</c>). Unknown sub-elements fall back to
+    ///     <see cref="ToDriverDataType"/> so the driver remains permissive.
+    /// </summary>
+    public static DriverDataType EffectiveDriverDataType(AbLegacyDataType t, string? subElement)
+    {
+        if (subElement is null) return t.ToDriverDataType();
+        var key = subElement.ToUpperInvariant();
+        return t switch
+        {
+            AbLegacyDataType.TimerElement => key switch
+            {
+                "EN" or "TT" or "DN" => DriverDataType.Boolean,
+                "PRE" or "ACC" => DriverDataType.Int32,
+                _ => t.ToDriverDataType(),
+            },
+            AbLegacyDataType.CounterElement => key switch
+            {
+                "CU" or "CD" or "DN" or "OV" or "UN" => DriverDataType.Boolean,
+                "PRE" or "ACC" => DriverDataType.Int32,
+                _ => t.ToDriverDataType(),
+            },
+            AbLegacyDataType.ControlElement => key switch
+            {
+                "EN" or "EU" or "DN" or "EM" or "ER" or "UL" or "IN" or "FD" => DriverDataType.Boolean,
+                "LEN" or "POS" => DriverDataType.Int32,
+                _ => t.ToDriverDataType(),
+            },
+            _ => t.ToDriverDataType(),
+        };
+    }
+
+    /// <summary>
+    ///     Bit position within the parent control word for Timer/Counter/Control status bits.
+    ///     Returns <c>null</c> if the sub-element is not a known bit member of the given element
+    ///     type. Bit numbering follows Rockwell DTAM / PCCC documentation.
+    /// </summary>
+    public static int? StatusBitIndex(AbLegacyDataType t, string? subElement)
+    {
+        if (subElement is null) return null;
+        var key = subElement.ToUpperInvariant();
+        return t switch
+        {
+            // T4 element word 0: bit 13=DN, 14=TT, 15=EN.
+            AbLegacyDataType.TimerElement => key switch
+            {
+                "DN" => 13,
+                "TT" => 14,
+                "EN" => 15,
+                _ => null,
+            },
+            // C5 element word 0: bit 10=UN, 11=OV, 12=DN, 13=CD, 14=CU.
+            AbLegacyDataType.CounterElement => key switch
+            {
+                "UN" => 10,
+                "OV" => 11,
+                "DN" => 12,
+                "CD" => 13,
+                "CU" => 14,
+                _ => null,
+            },
+            // R6 element word 0: bit 8=FD, 9=IN, 10=UL, 11=ER, 12=EM, 13=DN, 14=EU, 15=EN.
+            AbLegacyDataType.ControlElement => key switch
+            {
+                "FD" => 8,
+                "IN" => 9,
+                "UL" => 10,
+                "ER" => 11,
+                "EM" => 12,
+                "DN" => 13,
+                "EU" => 14,
+                "EN" => 15,
+                _ => null,
+            },
+            _ => null,
+        };
+    }
+
+    /// <summary>
+    ///     PLC-set status bits — read-only from the OPC UA side. Operator-controllable bits
+    ///     (e.g. <c>.EN</c> on a timer/counter, <c>.CU</c>/<c>.CD</c> rung-driven inputs) are
+    ///     omitted so they keep default writable behaviour.
+    /// </summary>
+    public static bool IsPlcSetStatusBit(AbLegacyDataType t, string? subElement)
+    {
+        if (subElement is null) return false;
+        var key = subElement.ToUpperInvariant();
+        return t switch
+        {
+            AbLegacyDataType.TimerElement => key is "DN" or "TT",
+            AbLegacyDataType.CounterElement => key is "DN" or "OV" or "UN",
+            AbLegacyDataType.ControlElement => key is "DN" or "EM" or "ER" or "FD" or "UL" or "IN",
+            _ => false,
+        };
+    }
 }
diff --git a/src/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/AbLegacyDriver.cs b/src/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/AbLegacyDriver.cs
index bef7957..86469b4 100644
--- a/src/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/AbLegacyDriver.cs
+++ b/src/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/AbLegacyDriver.cs
@@ -141,7 +141,12 @@ public sealed class AbLegacyDriver : IDriver, IReadable, IWritable, ITagDiscover
                 }
 
                 var parsed = AbLegacyAddress.TryParse(def.Address, device.Options.PlcFamily);
-                var value = runtime.DecodeValue(def.DataType, parsed?.BitIndex);
+                // Timer/Counter/Control status bits route through GetBit at the parent-word
+                // address — translate the .DN/.EN/etc. sub-element to its standard bit position
+                // and pass it down to the runtime as a synthetic bitIndex.
+                var decodeBit = parsed?.BitIndex
+                    ?? AbLegacyDataTypeExtensions.StatusBitIndex(def.DataType, parsed?.SubElement);
+                var value = runtime.DecodeValue(def.DataType, decodeBit);
                 results[i] = new DataValueSnapshot(value, AbLegacyStatusMapper.Good, now, now);
                 _health = new DriverHealth(DriverState.Healthy, now, null);
             }
@@ -188,6 +193,15 @@ public sealed class AbLegacyDriver : IDriver, IReadable, IWritable, ITagDiscover
             {
                 var parsed = AbLegacyAddress.TryParse(def.Address, device.Options.PlcFamily);
 
+                // Timer/Counter/Control PLC-set status bits (DN, TT, OV, UN, FD, ER, EM, UL,
+                // IN) are read-only — the PLC sets them; any client write would be silently
+                // overwritten on the next scan. Reject up front with BadNotWritable.
+                if (AbLegacyDataTypeExtensions.IsPlcSetStatusBit(def.DataType, parsed?.SubElement))
+                {
+                    results[i] = new WriteResult(AbLegacyStatusMapper.BadNotWritable);
+                    continue;
+                }
+
                 // PCCC bit-within-word writes — task #181 pass 2. RMW against a parallel
                 // parent-word runtime (strip the /N bit suffix). Per-parent-word lock serialises
                 // concurrent bit writers. Applies to N-file bit-in-word (N7:0/3) + B-file bits
@@ -247,12 +261,19 @@ public sealed class AbLegacyDriver : IDriver, IReadable, IWritable, ITagDiscover
                 string.Equals(t.DeviceHostAddress, device.HostAddress, StringComparison.OrdinalIgnoreCase));
             foreach (var tag in tagsForDevice)
             {
+                var parsed = AbLegacyAddress.TryParse(tag.Address, device.PlcFamily);
+                // Timer/Counter/Control sub-elements (.DN/.EN/.TT/.PRE/.ACC/etc.) refine the
+                // base element's Int32 to Boolean for status bits and Int32 for word members.
+                var effectiveType = AbLegacyDataTypeExtensions.EffectiveDriverDataType(
+                    tag.DataType, parsed?.SubElement);
+                var plcSetBit = AbLegacyDataTypeExtensions.IsPlcSetStatusBit(
+                    tag.DataType, parsed?.SubElement);
                 deviceFolder.Variable(tag.Name, tag.Name, new DriverAttributeInfo(
                     FullName: tag.Name,
-                    DriverDataType: tag.DataType.ToDriverDataType(),
+                    DriverDataType: effectiveType,
                     IsArray: false,
                     ArrayDim: null,
-                    SecurityClass: tag.Writable
+                    SecurityClass: tag.Writable && !plcSetBit
                         ? SecurityClassification.Operate
                         : SecurityClassification.ViewOnly,
                     IsHistorized: false,
diff --git a/src/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/LibplctagLegacyTagRuntime.cs b/src/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/LibplctagLegacyTagRuntime.cs
index 3f8e1aa..556d3d7 100644
--- a/src/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/LibplctagLegacyTagRuntime.cs
+++ b/src/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/LibplctagLegacyTagRuntime.cs
@@ -40,8 +40,14 @@ internal sealed class LibplctagLegacyTagRuntime : IAbLegacyTagRuntime
         AbLegacyDataType.Long => _tag.GetInt32(0),
         AbLegacyDataType.Float => _tag.GetFloat32(0),
         AbLegacyDataType.String => _tag.GetString(0),
+        // Timer/Counter/Control sub-elements: bitIndex is the status bit position within the
+        // parent control word (encoded by AbLegacyDriver from the .DN / .EN / etc. sub-element
+        // name). Word members (.PRE / .ACC / .LEN / .POS) come through with bitIndex=null and
+        // decode as Int32 like before.
         AbLegacyDataType.TimerElement or AbLegacyDataType.CounterElement
-            or AbLegacyDataType.ControlElement => _tag.GetInt32(0),
+            or AbLegacyDataType.ControlElement => bitIndex is int statusBit
+                ? _tag.GetBit(statusBit)
+                : _tag.GetInt32(0),
         _ => null,
     };
 
diff --git a/tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/AbLegacyDriverTests.cs b/tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/AbLegacyDriverTests.cs
index 5935d22..86dc460 100644
--- a/tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/AbLegacyDriverTests.cs
+++ b/tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/AbLegacyDriverTests.cs
@@ -102,4 +102,96 @@ public sealed class AbLegacyDriverTests
         AbLegacyDataType.String.ToDriverDataType().ShouldBe(DriverDataType.String);
         AbLegacyDataType.TimerElement.ToDriverDataType().ShouldBe(DriverDataType.Int32);
     }
+
+    [Theory]
+    [InlineData(AbLegacyDataType.TimerElement, "EN", DriverDataType.Boolean)]
+    [InlineData(AbLegacyDataType.TimerElement, "TT", DriverDataType.Boolean)]
+    [InlineData(AbLegacyDataType.TimerElement, "DN", DriverDataType.Boolean)]
+    [InlineData(AbLegacyDataType.TimerElement, "PRE", DriverDataType.Int32)]
+    [InlineData(AbLegacyDataType.TimerElement, "ACC", DriverDataType.Int32)]
+    [InlineData(AbLegacyDataType.CounterElement, "CU", DriverDataType.Boolean)]
+    [InlineData(AbLegacyDataType.CounterElement, "CD", DriverDataType.Boolean)]
+    [InlineData(AbLegacyDataType.CounterElement, "DN", DriverDataType.Boolean)]
+    [InlineData(AbLegacyDataType.CounterElement, "OV", DriverDataType.Boolean)]
+    [InlineData(AbLegacyDataType.CounterElement, "UN", DriverDataType.Boolean)]
+    [InlineData(AbLegacyDataType.CounterElement, "PRE", DriverDataType.Int32)]
+    [InlineData(AbLegacyDataType.CounterElement, "ACC", DriverDataType.Int32)]
+    [InlineData(AbLegacyDataType.ControlElement, "EN", DriverDataType.Boolean)]
+    [InlineData(AbLegacyDataType.ControlElement, "EU", DriverDataType.Boolean)]
+    [InlineData(AbLegacyDataType.ControlElement, "DN", DriverDataType.Boolean)]
+    [InlineData(AbLegacyDataType.ControlElement, "EM", DriverDataType.Boolean)]
+    [InlineData(AbLegacyDataType.ControlElement, "ER", DriverDataType.Boolean)]
+    [InlineData(AbLegacyDataType.ControlElement, "UL", DriverDataType.Boolean)]
+    [InlineData(AbLegacyDataType.ControlElement, "IN", DriverDataType.Boolean)]
+    [InlineData(AbLegacyDataType.ControlElement, "FD", DriverDataType.Boolean)]
+    [InlineData(AbLegacyDataType.ControlElement, "LEN", DriverDataType.Int32)]
+    [InlineData(AbLegacyDataType.ControlElement, "POS", DriverDataType.Int32)]
+    public void EffectiveDriverDataType_resolves_subelements(
+        AbLegacyDataType dataType, string subElement, DriverDataType expected)
+    {
+        AbLegacyDataTypeExtensions.EffectiveDriverDataType(dataType, subElement).ShouldBe(expected);
+    }
+
+    [Fact]
+    public void EffectiveDriverDataType_unknown_subelement_falls_back_to_base()
+    {
+        // Permissive — keeps the driver from refusing tags whose sub-element we don't catalogue.
+        AbLegacyDataTypeExtensions.EffectiveDriverDataType(AbLegacyDataType.TimerElement, "BOGUS")
+            .ShouldBe(DriverDataType.Int32);
+        AbLegacyDataTypeExtensions.EffectiveDriverDataType(AbLegacyDataType.TimerElement, null)
+            .ShouldBe(DriverDataType.Int32);
+        AbLegacyDataTypeExtensions.EffectiveDriverDataType(AbLegacyDataType.Int, "DN")
+            .ShouldBe(DriverDataType.Int32);
+    }
+
+    [Theory]
+    [InlineData(AbLegacyDataType.TimerElement, "DN", 13)]
+    [InlineData(AbLegacyDataType.TimerElement, "TT", 14)]
+    [InlineData(AbLegacyDataType.TimerElement, "EN", 15)]
+    [InlineData(AbLegacyDataType.CounterElement, "UN", 10)]
+    [InlineData(AbLegacyDataType.CounterElement, "OV", 11)]
+    [InlineData(AbLegacyDataType.CounterElement, "DN", 12)]
+    [InlineData(AbLegacyDataType.CounterElement, "CD", 13)]
+    [InlineData(AbLegacyDataType.CounterElement, "CU", 14)]
+    [InlineData(AbLegacyDataType.ControlElement, "FD", 8)]
+    [InlineData(AbLegacyDataType.ControlElement, "IN", 9)]
+    [InlineData(AbLegacyDataType.ControlElement, "UL", 10)]
+    [InlineData(AbLegacyDataType.ControlElement, "ER", 11)]
+    [InlineData(AbLegacyDataType.ControlElement, "EM", 12)]
+    [InlineData(AbLegacyDataType.ControlElement, "DN", 13)]
+    [InlineData(AbLegacyDataType.ControlElement, "EU", 14)]
+    [InlineData(AbLegacyDataType.ControlElement, "EN", 15)]
+    public void StatusBitIndex_maps_to_standard_pccc_positions(
+        AbLegacyDataType dataType, string subElement, int expectedBit)
+    {
+        AbLegacyDataTypeExtensions.StatusBitIndex(dataType, subElement).ShouldBe(expectedBit);
+    }
+
+    [Fact]
+    public void StatusBitIndex_for_word_subelements_is_null()
+    {
+        AbLegacyDataTypeExtensions.StatusBitIndex(AbLegacyDataType.TimerElement, "PRE").ShouldBeNull();
+        AbLegacyDataTypeExtensions.StatusBitIndex(AbLegacyDataType.CounterElement, "ACC").ShouldBeNull();
+        AbLegacyDataTypeExtensions.StatusBitIndex(AbLegacyDataType.ControlElement, "LEN").ShouldBeNull();
+        AbLegacyDataTypeExtensions.StatusBitIndex(AbLegacyDataType.TimerElement, null).ShouldBeNull();
+        AbLegacyDataTypeExtensions.StatusBitIndex(AbLegacyDataType.Int, "DN").ShouldBeNull();
+    }
+
+    [Theory]
+    [InlineData(AbLegacyDataType.TimerElement, "DN", true)]
+    [InlineData(AbLegacyDataType.TimerElement, "TT", true)]
+    [InlineData(AbLegacyDataType.TimerElement, "EN", false)] // operator-controllable
+    [InlineData(AbLegacyDataType.CounterElement, "DN", true)]
+    [InlineData(AbLegacyDataType.CounterElement, "OV", true)]
+    [InlineData(AbLegacyDataType.CounterElement, "UN", true)]
+    [InlineData(AbLegacyDataType.CounterElement, "CU", false)]
+    [InlineData(AbLegacyDataType.ControlElement, "DN", true)]
+    [InlineData(AbLegacyDataType.ControlElement, "ER", true)]
+    [InlineData(AbLegacyDataType.ControlElement, "EM", true)]
+    [InlineData(AbLegacyDataType.ControlElement, "EN", false)]
+    public void IsPlcSetStatusBit_classifies_writable_vs_status_bits(
+        AbLegacyDataType dataType, string subElement, bool expected)
+    {
+        AbLegacyDataTypeExtensions.IsPlcSetStatusBit(dataType, subElement).ShouldBe(expected);
+    }
 }
diff --git a/tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/AbLegacyReadWriteTests.cs b/tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/AbLegacyReadWriteTests.cs
index b71ade6..c9eed25 100644
--- a/tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/AbLegacyReadWriteTests.cs
+++ b/tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/AbLegacyReadWriteTests.cs
@@ -256,4 +256,113 @@ public sealed class AbLegacyReadWriteTests
             Value = value;
         }
     }
+
+    // ---- Timer / Counter / Control sub-element bit semantics (issue #246) ----
+
+    [Theory]
+    [InlineData("T4:0.DN", 13)]
+    [InlineData("T4:0.TT", 14)]
+    [InlineData("T4:0.EN", 15)]
+    public async Task Timer_status_bit_decodes_correct_position(string address, int bitPos)
+    {
+        var (drv, factory) = NewDriver(
+            new AbLegacyTagDefinition("X", "ab://10.0.0.5/1,0", address, AbLegacyDataType.TimerElement));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        // Seed a parent-word with only the target bit set.
+        factory.Customise = p => new FakeAbLegacyTag(p) { Value = 1 << bitPos };
+
+        var snapshots = await drv.ReadAsync(["X"], CancellationToken.None);
+
+        snapshots.Single().Value.ShouldBe(true);
+        // The driver must have asked the runtime for the right bit position.
+        factory.Tags[address].LastDecodeBitIndex.ShouldBe(bitPos);
+    }
+
+    [Fact]
+    public async Task Timer_PRE_subelement_decodes_as_int_word()
+    {
+        var (drv, factory) = NewDriver(
+            new AbLegacyTagDefinition("Pre", "ab://10.0.0.5/1,0", "T4:0.PRE", AbLegacyDataType.TimerElement));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        factory.Customise = p => new FakeAbLegacyTag(p) { Value = 5000 };
+
+        var snapshots = await drv.ReadAsync(["Pre"], CancellationToken.None);
+
+        snapshots.Single().Value.ShouldBe(5000);
+        factory.Tags["T4:0.PRE"].LastDecodeBitIndex.ShouldBeNull();
+    }
+
+    [Theory]
+    [InlineData("C5:0.UN", 10)]
+    [InlineData("C5:0.OV", 11)]
+    [InlineData("C5:0.DN", 12)]
+    [InlineData("C5:0.CD", 13)]
+    [InlineData("C5:0.CU", 14)]
+    public async Task Counter_status_bit_decodes_correct_position(string address, int bitPos)
+    {
+        var (drv, factory) = NewDriver(
+            new AbLegacyTagDefinition("X", "ab://10.0.0.5/1,0", address, AbLegacyDataType.CounterElement));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        factory.Customise = p => new FakeAbLegacyTag(p) { Value = 1 << bitPos };
+
+        var snapshots = await drv.ReadAsync(["X"], CancellationToken.None);
+        snapshots.Single().Value.ShouldBe(true);
+        factory.Tags[address].LastDecodeBitIndex.ShouldBe(bitPos);
+    }
+
+    [Theory]
+    [InlineData("R6:0.FD", 8)]
+    [InlineData("R6:0.IN", 9)]
+    [InlineData("R6:0.UL", 10)]
+    [InlineData("R6:0.ER", 11)]
+    [InlineData("R6:0.EM", 12)]
+    [InlineData("R6:0.DN", 13)]
+    [InlineData("R6:0.EU", 14)]
+    [InlineData("R6:0.EN", 15)]
+    public async Task Control_status_bit_decodes_correct_position(string address, int bitPos)
+    {
+        var (drv, factory) = NewDriver(
+            new AbLegacyTagDefinition("X", "ab://10.0.0.5/1,0", address, AbLegacyDataType.ControlElement));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        factory.Customise = p => new FakeAbLegacyTag(p) { Value = 1 << bitPos };
+
+        var snapshots = await drv.ReadAsync(["X"], CancellationToken.None);
+        snapshots.Single().Value.ShouldBe(true);
+        factory.Tags[address].LastDecodeBitIndex.ShouldBe(bitPos);
+    }
+
+    [Fact]
+    public async Task Status_bit_returns_false_when_parent_word_bit_is_clear()
+    {
+        var (drv, factory) = NewDriver(
+            new AbLegacyTagDefinition("Done", "ab://10.0.0.5/1,0", "T4:0.DN", AbLegacyDataType.TimerElement));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        // Bit 14 (TT) set, bit 13 (DN) clear.
+        factory.Customise = p => new FakeAbLegacyTag(p) { Value = 1 << 14 };
+
+        var snapshots = await drv.ReadAsync(["Done"], CancellationToken.None);
+        snapshots.Single().Value.ShouldBe(false);
+    }
+
+    [Theory]
+    [InlineData("T4:0.DN", AbLegacyDataType.TimerElement)]
+    [InlineData("T4:0.TT", AbLegacyDataType.TimerElement)]
+    [InlineData("C5:0.DN", AbLegacyDataType.CounterElement)]
+    [InlineData("C5:0.OV", AbLegacyDataType.CounterElement)]
+    [InlineData("C5:0.UN", AbLegacyDataType.CounterElement)]
+    [InlineData("R6:0.ER", AbLegacyDataType.ControlElement)]
+    [InlineData("R6:0.EM", AbLegacyDataType.ControlElement)]
+    [InlineData("R6:0.DN", AbLegacyDataType.ControlElement)]
+    [InlineData("R6:0.FD", AbLegacyDataType.ControlElement)]
+    public async Task Writes_to_PLC_set_status_bits_return_BadNotWritable(
+        string address, AbLegacyDataType dataType)
+    {
+        var (drv, _) = NewDriver(
+            new AbLegacyTagDefinition("X", "ab://10.0.0.5/1,0", address, dataType));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var results = await drv.WriteAsync(
+            [new WriteRequest("X", true)], CancellationToken.None);
+        results.Single().StatusCode.ShouldBe(AbLegacyStatusMapper.BadNotWritable);
+    }
 }
diff --git a/tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/FakeAbLegacyTag.cs b/tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/FakeAbLegacyTag.cs
index 914fa8f..14b6a0e 100644
--- a/tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/FakeAbLegacyTag.cs
+++ b/tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/FakeAbLegacyTag.cs
@@ -40,7 +40,25 @@ internal class FakeAbLegacyTag : IAbLegacyTagRuntime
     }
 
     public virtual int GetStatus() => Status;
-    public virtual object? DecodeValue(AbLegacyDataType type, int? bitIndex) => Value;
+    public int? LastDecodeBitIndex { get; private set; }
+    public AbLegacyDataType? LastDecodeType { get; private set; }
+    public virtual object? DecodeValue(AbLegacyDataType type, int? bitIndex)
+    {
+        LastDecodeType = type;
+        LastDecodeBitIndex = bitIndex;
+        // If the test seeded a parent-word value (ushort/short/int) and the driver asked for a
+        // specific status bit, mask it out so we can assert the correct bit reaches the client.
+        if (bitIndex is int bit && Value is not null and not bool)
+        {
+            try
+            {
+                var word = Convert.ToInt32(Value);
+                return ((word >> bit) & 1) != 0;
+            }
+            catch (Exception ex) when (ex is FormatException or InvalidCastException) { }
+        }
+        return Value;
+    }
     public virtual void EncodeValue(AbLegacyDataType type, int? bitIndex, object? value) => Value = value;
     public virtual void Dispose() => Disposed = true;
 }