diff --git a/src/line_laser_modbus/client.py b/src/line_laser_modbus/client.py
index 03518e4..46ec9cd 100644
--- a/src/line_laser_modbus/client.py
+++ b/src/line_laser_modbus/client.py
@@ -16,6 +16,7 @@ from line_laser_modbus.codec import (
 )
 from line_laser_modbus.config import SerialConfig
 from line_laser_modbus.constants import (
+    ADDR_AVAILABLE_CACHE_COUNT,
     ADDR_CORRECTION,
     ADDR_CURRENT_POSE,
     ADDR_DEVICE_STATUS,
@@ -133,6 +134,11 @@ class LineLaserClient:
 
         return ensure_status(self._read_word(ADDR_DEVICE_STATUS))
 
+    def read_available_cache_count(self) -> int:
+        """读取 0xD002 目标位姿可用缓存数量"""
+
+        return self._read_word(ADDR_AVAILABLE_CACHE_COUNT)
+
     def read_current_pose(self) -> Pose6D:
         """读取控制器当前 XYZABC 位姿"""
 
@@ -168,6 +174,9 @@ class LineLaserClient:
     def write_target_timed_pose(self, data: TimedPose6D) -> None:
         """写入示教目标时间戳和 XYZABC 位姿"""
 
+        if self.read_available_cache_count() <= 0:
+            msg = "Target pose cache is full; available cache count at 0xD002 is 0"
+            raise RuntimeError(msg)
         self._write_registers(ADDR_TARGET_POSE, encode_timed_pose(data))
 
     def write_correction(self, pose: Pose6D, *, timestamp: int = 0) -> None:
diff --git a/src/line_laser_modbus/constants.py b/src/line_laser_modbus/constants.py
index 88e2668..5fe16e3 100644
--- a/src/line_laser_modbus/constants.py
+++ b/src/line_laser_modbus/constants.py
@@ -9,7 +9,8 @@ FUNC_WRITE_MULTIPLE_REGISTERS = 0x10
 # 保持寄存器绝对地址。
 ADDR_MODE_COMMAND = 0xD000
 ADDR_DEVICE_STATUS = 0xD001
-ADDR_EXTENSION_RESERVED_1_START = 0xD002
+ADDR_AVAILABLE_CACHE_COUNT = 0xD002
+ADDR_EXTENSION_RESERVED_1_START = 0xD003
 ADDR_EXTENSION_RESERVED_1_END = 0xD009
 ADDR_CURRENT_POSE = 0xD00A
 ADDR_EXTENSION_RESERVED_2_START = 0xD018
@@ -28,6 +29,7 @@ REGISTER_COUNT_WORD = 1
 REGISTER_COUNT_TIMESTAMP = 2
 REGISTER_COUNT_AXES = 12
 REGISTER_COUNT_POSE = 14
+REGISTER_COUNT_EXTENSION_RESERVED_1 = 7
 REGISTER_COUNT_EXTENSION_RESERVED = 8
 REGISTER_COUNT_CALIBRATION_RESERVED = 32
 AXIS_NAMES = ("x", "y", "z", "a", "b", "c")
diff --git a/src/line_laser_modbus/simulator.py b/src/line_laser_modbus/simulator.py
index 4a48039..3f0f069 100644
--- a/src/line_laser_modbus/simulator.py
+++ b/src/line_laser_modbus/simulator.py
@@ -4,8 +4,9 @@ from __future__ import annotations
 
 from dataclasses import dataclass
 
-from line_laser_modbus.codec import decode_pose, encode_pose
+from line_laser_modbus.codec import decode_pose, encode_pose, encode_u16
 from line_laser_modbus.constants import (
+    ADDR_AVAILABLE_CACHE_COUNT,
     ADDR_CORRECTION,
     ADDR_CURRENT_POSE,
     ADDR_DEVICE_STATUS,
@@ -50,6 +51,7 @@ class SimulatedModbusBackend:
         slave_id: int = SLAVE_ID,
         mode: ModeCommand = ModeCommand.MANUAL_TEACHING,
         status: DeviceStatus = DeviceStatus.IDLE,
+        available_cache_count: int = 1,
         current_pose: Pose6D | None = None,
     ) -> None:
         """创建模拟后端并写入初始寄存器值"""
@@ -57,7 +59,7 @@ class SimulatedModbusBackend:
         self.slave_id = slave_id
         self.connected = False
         self.registers: dict[int, int] = {}
-        self._seed(mode, status, current_pose or Pose6D.zeros())
+        self._seed(mode, status, available_cache_count, current_pose or Pose6D.zeros())
 
     def connect(self) -> bool:
         """标记模拟后端为已连接"""
@@ -94,11 +96,18 @@ class SimulatedModbusBackend:
 
         return self._read_pose(ADDR_CORRECTION)
 
-    def _seed(self, mode: ModeCommand, status: DeviceStatus, pose: Pose6D) -> None:
+    def _seed(
+        self,
+        mode: ModeCommand,
+        status: DeviceStatus,
+        available_cache_count: int,
+        pose: Pose6D,
+    ) -> None:
         """写入模拟器初始模式状态和当前位姿"""
 
         self.registers[ADDR_MODE_COMMAND] = mode.value
         self.registers[ADDR_DEVICE_STATUS] = status.value
+        self.registers[ADDR_AVAILABLE_CACHE_COUNT] = encode_u16(available_cache_count)
         for offset, value in enumerate(encode_pose(pose)):
             self.registers[ADDR_CURRENT_POSE + offset] = value
 
diff --git a/tests/test_client_simulator.py b/tests/test_client_simulator.py
index c0b049c..2e1cc86 100644
--- a/tests/test_client_simulator.py
+++ b/tests/test_client_simulator.py
@@ -3,6 +3,7 @@ import pytest
 from line_laser_modbus.client import LineLaserClient
 from line_laser_modbus.config import SerialConfig
 from line_laser_modbus.constants import (
+    ADDR_AVAILABLE_CACHE_COUNT,
     ADDR_CORRECTION,
     ADDR_CURRENT_POSE,
     ADDR_MODE_COMMAND,
@@ -31,6 +32,7 @@ def test_client_reads_seeded_status_and_pose_from_simulator() -> None:
 
     with LineLaserClient(SerialConfig(port="SIM"), backend=backend) as client:
         assert client.read_status() is DeviceStatus.TRACKING_OK
+        assert client.read_available_cache_count() == 1
         assert client.read_current_pose() == pose
         timed_pose = client.read_current_timed_pose()
         assert timed_pose.timestamp == 0
@@ -92,6 +94,20 @@ def test_client_writes_timed_target_pose_to_simulator() -> None:
     assert backend.registers[ADDR_TARGET_POSE + 1] == 0x04D2
 
 
+def test_client_rejects_target_pose_when_cache_is_full() -> None:
+    backend = SimulatedModbusBackend(available_cache_count=0)
+    target = TimedPose6D(1234, Pose6D(1.0, 2.0, 3.0, 4.0, 5.0, 6.0))
+
+    with (
+        pytest.raises(RuntimeError, match="Target pose cache is full"),
+        LineLaserClient(SerialConfig(port="SIM"), backend=backend) as client,
+    ):
+        client.write_target_timed_pose(target)
+
+    assert ADDR_TARGET_POSE not in backend.registers
+    assert backend.registers[ADDR_AVAILABLE_CACHE_COUNT] == 0
+
+
 def test_client_writes_timed_correction_to_simulator() -> None:
     backend = SimulatedModbusBackend()
     correction = TimedPose6D(1000, Pose6D(1.0, 2.0, 3.0, 0.0, 1.0, 2.0))
diff --git a/tests/test_constants.py b/tests/test_constants.py
index efc66a8..afcc188 100644
--- a/tests/test_constants.py
+++ b/tests/test_constants.py
@@ -1,4 +1,5 @@
 from line_laser_modbus.constants import (
+    ADDR_AVAILABLE_CACHE_COUNT,
     ADDR_CALIBRATION_RESERVED_END,
     ADDR_CALIBRATION_RESERVED_START,
     ADDR_CORRECTION,
@@ -14,6 +15,7 @@ from line_laser_modbus.constants import (
     ADDR_TARGET_POSE,
     REGISTER_COUNT_CALIBRATION_RESERVED,
     REGISTER_COUNT_EXTENSION_RESERVED,
+    REGISTER_COUNT_EXTENSION_RESERVED_1,
     REGISTER_COUNT_POSE,
 )
 
@@ -25,6 +27,7 @@ def test_calibration_reserved_range_matches_protocol() -> None:
 
 
 def test_pose_ranges_match_protocol() -> None:
+    assert ADDR_AVAILABLE_CACHE_COUNT == 0xD002
     assert ADDR_CURRENT_POSE == 0xD00A
     assert ADDR_TARGET_POSE == 0xD020
     assert ADDR_CORRECTION == 0xD036
@@ -33,11 +36,15 @@ def test_pose_ranges_match_protocol() -> None:
 
 def test_extension_reserved_ranges_match_protocol() -> None:
     ranges = [
-        (ADDR_EXTENSION_RESERVED_1_START, ADDR_EXTENSION_RESERVED_1_END, 0xD002, 0xD009),
         (ADDR_EXTENSION_RESERVED_2_START, ADDR_EXTENSION_RESERVED_2_END, 0xD018, 0xD01F),
         (ADDR_EXTENSION_RESERVED_3_START, ADDR_EXTENSION_RESERVED_3_END, 0xD02E, 0xD035),
         (ADDR_EXTENSION_RESERVED_4_START, ADDR_EXTENSION_RESERVED_4_END, 0xD044, 0xD04B),
     ]
+    assert ADDR_EXTENSION_RESERVED_1_START == 0xD003
+    assert ADDR_EXTENSION_RESERVED_1_END == 0xD009
+    assert ADDR_EXTENSION_RESERVED_1_END - ADDR_EXTENSION_RESERVED_1_START + 1 == (
+        REGISTER_COUNT_EXTENSION_RESERVED_1
+    )
     for start, end, expected_start, expected_end in ranges:
         assert start == expected_start
         assert end == expected_end