diff --git a/doc/iidxhook/iidxio-ezusb.md b/doc/iidxhook/iidxio-ezusb.md
index ca893ce..981e04b 100644
--- a/doc/iidxhook/iidxio-ezusb.md
+++ b/doc/iidxhook/iidxio-ezusb.md
@@ -1,4 +1,4 @@
-This library drives a "legacy" ezusb IO board, also known as C02 IO, and 
+This library drives a "legacy" ezusb IO board, also known as C02/D01 IO, and 
 implements the iidxio API of BT5. Thus, it allows you to use this IO board with
 *any* version of IIDX that is supported by BT5.
 
@@ -24,5 +24,7 @@ the status LEDs on the side of the board should show a blinking pattern.
 dump to the FPGA.
 * There is a script called ezusb-boot.bat which combines the two steps above
 and can be integrated into the startup process of a dedicated setup.
+* If you are using a D01 IO board, use the `fpga-d01.bin` file instead of the
+`fpga.bin` file.
 * If you ignore these steps, you will either run into errors or parts of the
 IO board won't work (e.g. lights).
\ No newline at end of file
diff --git a/src/main/ezusb-iidx-emu/msg.c b/src/main/ezusb-iidx-emu/msg.c
index c7dafcb..c651042 100644
--- a/src/main/ezusb-iidx-emu/msg.c
+++ b/src/main/ezusb-iidx-emu/msg.c
@@ -160,6 +160,10 @@ static HRESULT ezusb_iidx_emu_msg_interrupt_read(struct iobuf *read)
     otherwise the game's fpga check will fail */
     msg_resp->fpga2_check_flag_unkn = 2;
 
+#ifdef EZUSB_IIDX_EMU_D01_BOARD
+    msg_resp->inverted_pad &= ~(1 << 4);
+#endif
+
     read->pos = sizeof(*msg_resp);
 
     return S_OK;
diff --git a/src/main/ezusb-iidx/msg.h b/src/main/ezusb-iidx/msg.h
index 718f149..5f81f8d 100644
--- a/src/main/ezusb-iidx/msg.h
+++ b/src/main/ezusb-iidx/msg.h
@@ -59,7 +59,9 @@ struct ezusb_iidx_msg_interrupt_read_packet {
       1: Not used
       2: Not used
       3: Not used
-      4: Not used
+      4: C02/D01 board identifier, 1 = C02, 0 = D01 (on active low). This defines how the game has
+         to flash the FPGA board since D01 needs a different firmware (see result of FPGA CHECK on
+         game bootup)
       5: Not used
       6: usb mute?
       7: Not used
diff --git a/src/main/iidxio-ezusb/iidxio.c b/src/main/iidxio-ezusb/iidxio.c
index 3852582..0a74a29 100644
--- a/src/main/iidxio-ezusb/iidxio.c
+++ b/src/main/iidxio-ezusb/iidxio.c
@@ -192,7 +192,8 @@ uint8_t iidx_io_ep2_get_slider(uint8_t slider_no)
 
 uint8_t iidx_io_ep2_get_sys(void)
 {
-    return ((~iidx_io_ezusb_read_packet.inverted_pad) >> 28) & 0x03;
+    return (((~iidx_io_ezusb_read_packet.inverted_pad) >> 28) & 0x03) |
+        ((((~iidx_io_ezusb_read_packet.inverted_pad) >> 22) & 0x01) << 2);
 }
 
 uint8_t iidx_io_ep2_get_panel(void)