diff --git a/pm3py/core/hf_iso15.py b/pm3py/core/hf_iso15.py
index 40e3c2d..090b4ed 100644
--- a/pm3py/core/hf_iso15.py
+++ b/pm3py/core/hf_iso15.py
@@ -1,6 +1,6 @@
 """ISO 15693 commands: hf.iso15.*"""
 import struct
-from .protocol import Cmd
+from .protocol import Cmd, crc15_bytes
 from .transport import PM3Transport, PM3Error
 
 # Re-export trace symbols for backward compat with existing test imports
@@ -11,12 +11,28 @@ from ..trace import (
     format_sniff_line,
 )
 
-# ISO15 PM3 flags
+# ISO15 PM3 transport flags — values MUST match firmware include/iso15.h
 ISO15_CONNECT = 0x01
 ISO15_NO_DISCONNECT = 0x02
 ISO15_RAW = 0x04
-ISO15_APPEND_CRC = 0x08
-ISO15_READ_RESPONSE = 0x10
+ISO15_APPEND_CRC = 0x08        # legacy: ARM firmware ignores it — CRC is added host-side
+ISO15_HIGH_SPEED = 0x10
+ISO15_READ_RESPONSE = 0x20
+ISO15_LONG_WAIT = 0x40
+
+
+def _iso15_payload(iso_cmd: bytes) -> bytes:
+    """Build a HF_ISO15693_COMMAND payload from a raw ISO15693 command.
+
+    Appends the ISO15693 CRC host-side (the ARM firmware ignores ISO15_APPEND_CRC —
+    the client must add it, like the C client's AddCrc15) and prefixes the PM3 transport
+    flags. HIGH_SPEED + READ_RESPONSE make the firmware receive at high data rate and
+    actually listen for the tag's answer — without READ_RESPONSE (0x20) the firmware
+    passes a NULL rx buffer and replies empty.
+    """
+    raw = iso_cmd + crc15_bytes(iso_cmd)
+    flags = ISO15_CONNECT | ISO15_HIGH_SPEED | ISO15_READ_RESPONSE
+    return struct.pack("<BH", flags, len(raw)) + raw
 
 
 class HF15Commands:
@@ -33,8 +49,7 @@ class HF15Commands:
         # so this parser would read the struct header as a zeroed UID. 1-slot gives the
         # simple single-tag response this method expects. Use hf 15 reader --all for many.
         iso_cmd = bytes([0x26, 0x01, 0x00])  # flags, inventory cmd, mask_len=0
-        flags = ISO15_CONNECT | ISO15_READ_RESPONSE | ISO15_APPEND_CRC
-        payload = struct.pack("<BH", flags, len(iso_cmd)) + iso_cmd
+        payload = _iso15_payload(iso_cmd)
         resp = await self._t.send_ng(Cmd.HF_ISO15693_COMMAND, payload, timeout=5.0)
 
         if resp.status != 0 or len(resp.data) < 10:
@@ -51,6 +66,17 @@ class HF15Commands:
             "response_flags": resp_flags,
         }
 
+    async def raw_inventory(self, inv_flags: int = 0x26) -> dict:
+        """Diagnostic: send a raw ISO15693 inventory with a caller-chosen request-flags
+        byte and return the raw device response (no parsing). Use to isolate 1-slot vs
+        16-slot behavior: inv_flags=0x26 → 1 slot (SLOT1 set), 0x06 → 16 slots.
+        """
+        iso_cmd = bytes([inv_flags, 0x01, 0x00])  # inv flags, INVENTORY cmd, mask_len=0
+        payload = _iso15_payload(iso_cmd)
+        resp = await self._t.send_ng(Cmd.HF_ISO15693_COMMAND, payload, timeout=5.0)
+        return {"inv_flags": hex(inv_flags), "status": resp.status,
+                "len": len(resp.data), "data": resp.data.hex()}
+
     async def rdbl(self, block: int, uid: str | None = None) -> dict:
         """Read a single block."""
         if uid:
@@ -59,8 +85,7 @@ class HF15Commands:
         else:
             iso_cmd = bytes([0x02, 0x20, block])  # addressed without UID
 
-        flags = ISO15_CONNECT | ISO15_READ_RESPONSE | ISO15_APPEND_CRC
-        payload = struct.pack("<BH", flags, len(iso_cmd)) + iso_cmd
+        payload = _iso15_payload(iso_cmd)
         resp = await self._t.send_ng(Cmd.HF_ISO15693_COMMAND, payload, timeout=5.0)
 
         if resp.status != 0 or len(resp.data) < 2:
@@ -92,8 +117,7 @@ class HF15Commands:
         else:
             iso_cmd = bytes([0x02, 0x21, block]) + data
 
-        flags = ISO15_CONNECT | ISO15_READ_RESPONSE | ISO15_APPEND_CRC
-        payload = struct.pack("<BH", flags, len(iso_cmd)) + iso_cmd
+        payload = _iso15_payload(iso_cmd)
         resp = await self._t.send_ng(Cmd.HF_ISO15693_COMMAND, payload, timeout=5.0)
 
         success = resp.status == 0 and len(resp.data) > 0 and resp.data[0] == 0
diff --git a/pm3py/core/protocol.py b/pm3py/core/protocol.py
index 79ba814..e866b05 100644
--- a/pm3py/core/protocol.py
+++ b/pm3py/core/protocol.py
@@ -68,6 +68,23 @@ def crc16_a(data: bytes) -> int:
     return crc
 
 
+def crc15(data: bytes) -> int:
+    """ISO 15693 / NFC Type 5 CRC (CRC-16/X-25): poly=0x8408 (reflected), init=0xFFFF,
+    refin/refout=true, xorout=0xFFFF. Check value crc15(b"123456789") == 0x906E."""
+    crc = 0xFFFF
+    for b in data:
+        crc ^= b
+        for _ in range(8):
+            crc = (crc >> 1) ^ 0x8408 if (crc & 1) else (crc >> 1)
+    return (~crc) & 0xFFFF
+
+
+def crc15_bytes(data: bytes) -> bytes:
+    """ISO 15693 CRC as appended on the wire (LSB byte first)."""
+    c = crc15(data)
+    return bytes([c & 0xFF, (c >> 8) & 0xFF])
+
+
 # --- Error codes ---
 class PM3Status(IntEnum):
     SUCCESS = 0
diff --git a/tests/test_crc.py b/tests/test_crc.py
index 4f1beb9..051ea83 100644
--- a/tests/test_crc.py
+++ b/tests/test_crc.py
@@ -1,4 +1,4 @@
-from pm3py.core.protocol import crc16_a
+from pm3py.core.protocol import crc16_a, crc15, crc15_bytes
 
 def test_crc16_a_empty():
     assert crc16_a(b"") == 0x6363  # init 0xC6C6 reflected = 0x6363
@@ -15,3 +15,20 @@ def test_crc16_a_ping_preamble():
     crc = crc16_a(preamble)
     assert isinstance(crc, int)
     assert 0 <= crc <= 0xFFFF
+
+
+def test_crc15_known_vector():
+    # ISO15693 / NFC Type 5 CRC == CRC-16/X-25; standard check string -> 0x906E
+    assert crc15(b"123456789") == 0x906E
+
+def test_crc15_residue():
+    # Appending crc15 (LSB-first) then re-running the raw X-25 loop over the full
+    # frame yields the X-25 residue 0xF0B8 — the property firmware CheckCrc15 uses.
+    data = bytes([0x26, 0x01, 0x00])
+    frame = data + crc15_bytes(data)
+    crc = 0xFFFF
+    for byte in frame:
+        crc ^= byte
+        for _ in range(8):
+            crc = (crc >> 1) ^ 0x8408 if (crc & 1) else (crc >> 1)
+    assert crc == 0xF0B8