diff --git a/src/laddercodec/csv/writer.py b/src/laddercodec/csv/writer.py
index 568cc2a..66aa25d 100644
--- a/src/laddercodec/csv/writer.py
+++ b/src/laddercodec/csv/writer.py
@@ -280,11 +280,17 @@ def _emit_drum_block(
             f".jump({drum.jump_target})",
         )
     else:
-        data_row_count = _emit_blank_continuation(rows, data_row_count, condition_rows[start + 2])
+        # Drum continuation rows are positional.  Omitting an empty jump row
+        # lets a later blank-AF row slide into the jump/jog slot on reparse.
+        data_row_count = _append_data_row(
+            rows, data_row_count, condition_rows[start + 2], ""
+        )
     if drum.jog_enabled:
         data_row_count = _append_data_row(rows, data_row_count, condition_rows[start + 3], ".jog()")
     else:
-        data_row_count = _emit_blank_continuation(rows, data_row_count, condition_rows[start + 3])
+        data_row_count = _append_data_row(
+            rows, data_row_count, condition_rows[start + 3], ""
+        )
     return data_row_count, 4
 
 
diff --git a/src/laddercodec/instructions/drum.py b/src/laddercodec/instructions/drum.py
index f4d1cb7..65e9608 100644
--- a/src/laddercodec/instructions/drum.py
+++ b/src/laddercodec/instructions/drum.py
@@ -342,7 +342,10 @@ def parse_af_call(call: AfCall) -> Drum:
         events_or_presets = _parse_simple_list(call.kwargs.get("presets", "[]"))
         accumulator = call.kwargs.get("accumulator", "")
         unit = call.kwargs.get("unit", "")
-        if unit not in _TIME_FC:
+        # CSV parsing and round-trip validation do not build a binary blob.
+        # Accept every unit the decoder can emit, even when binary encoding for
+        # that unit is not implemented in ``_TIME_FC`` yet.
+        if unit not in _DRUM_UNIT_TO_INDEX:
             raise ValueError(f"Unsupported time drum unit: {unit!r}")
 
     return Drum(
diff --git a/tests/csv/test_converter.py b/tests/csv/test_converter.py
index 74a7ccc..5378852 100644
--- a/tests/csv/test_converter.py
+++ b/tests/csv/test_converter.py
@@ -30,6 +30,7 @@
     CompareContact,
     Contact,
     Counter,
+    Drum,
     ForLoop,
     Next,
     RawInstruction,
@@ -335,7 +336,8 @@ def test_timer_rejects_unknown_unit(self) -> None:
         with pytest.raises(ValueError, match="Unknown timer unit"):
             af_node_to_token(node)
 
-    def test_time_drum_rejects_unsupported_unit(self) -> None:
+    @pytest.mark.parametrize("unit", ["Tms", "Ts", "Tm", "Th", "Td"])
+    def test_time_drum_accepts_known_unit(self, unit: str) -> None:
         node = AfCall(
             name="time_drum",
             args=(),
@@ -343,7 +345,26 @@ def test_time_drum_rejects_unsupported_unit(self) -> None:
             kwargs={
                 "outputs": "[C211,C212]",
                 "presets": "[100,200]",
-                "unit": "Ts",
+                "unit": unit,
+                "pattern": "[[1,0],[0,1]]",
+                "current_step": "DS186",
+                "accumulator": "TD5",
+                "completion_flag": "C213",
+            },
+        )
+        result = af_node_to_token(node)
+        assert isinstance(result, Drum)
+        assert result.unit == unit
+
+    def test_time_drum_rejects_unknown_unit(self) -> None:
+        node = AfCall(
+            name="time_drum",
+            args=(),
+            known=True,
+            kwargs={
+                "outputs": "[C211,C212]",
+                "presets": "[100,200]",
+                "unit": "BadUnit",
                 "pattern": "[[1,0],[0,1]]",
                 "current_step": "DS186",
                 "accumulator": "TD5",
diff --git a/tests/csv/test_writer.py b/tests/csv/test_writer.py
index 6cec404..866ce0b 100644
--- a/tests/csv/test_writer.py
+++ b/tests/csv/test_writer.py
@@ -23,6 +23,7 @@
 )
 from laddercodec.csv.writer import (
     WriterError,
+    _rebuild_rung_from_rows,
     _validate_roundtrip,
     decoded_rung_to_rows,
 )
@@ -241,6 +242,61 @@ def test_timer_retained_emits_reset_pin(self) -> None:
         assert rows[1][0] == ""
         assert rows[1][32] == ".reset()"
 
+    @pytest.mark.parametrize("unit", ["Ts", "Tm", "Th"])
+    def test_time_drum_known_unit_roundtrips_to_csv(self, unit: str) -> None:
+        drum = Drum(
+            drum_kind="time",
+            outputs=["C206", "C207"],
+            events_or_presets=["100", "200"],
+            pattern=[[1, 0], [0, 1]],
+            current_step="DS186",
+            completion_flag="C213",
+            accumulator="TD5",
+            unit=unit,
+        )
+        rung = Rung(
+            logical_rows=4,
+            conditions=[_contact_row("C210"), *([_blank_conditions()] * 3)],
+            instructions=[drum, "", "", ""],
+            comment_rtf=None,
+            comment=None,
+        )
+
+        rows = decoded_rung_to_rows(rung)
+
+        assert f"unit={unit}" in rows[0][32]
+
+    def test_time_drum_preserves_blank_pin_slots_before_following_rows(self) -> None:
+        drum = Drum(
+            drum_kind="time",
+            outputs=["C1056", "C1057"],
+            events_or_presets=["10", "600"],
+            pattern=[[1, 0], [0, 1]],
+            current_step="DS6",
+            completion_flag="C109",
+            accumulator="TD4",
+            unit="Ts",
+        )
+        rung = Rung(
+            logical_rows=5,
+            conditions=[
+                _contact_row("C108"),
+                _contact_row("C109"),
+                _blank_conditions(),
+                _contact_row("C110"),
+                _contact_row("C111"),
+            ],
+            instructions=[drum, "", "", "", ""],
+            comment_rtf=None,
+            comment=None,
+        )
+
+        rows = decoded_rung_to_rows(rung)
+        rebuilt = _rebuild_rung_from_rows(rows)
+
+        assert rebuilt.logical_rows == 5
+        assert rebuilt.conditions == rung.conditions
+
     def test_nop(self) -> None:
         """NOP token serializes correctly."""
         rung = Rung(