diff --git a/boards/uniboard2/designs/unb2_test/src/vhdl/unb2_test.vhd b/boards/uniboard2/designs/unb2_test/src/vhdl/unb2_test.vhd
index 72f970100c9817e4b62249f01d82714b2c731a3f..52060a9656314303d8468e4503dd8434b601cdf7 100644
--- a/boards/uniboard2/designs/unb2_test/src/vhdl/unb2_test.vhd
+++ b/boards/uniboard2/designs/unb2_test/src/vhdl/unb2_test.vhd
@@ -285,6 +285,8 @@ ARCHITECTURE str OF unb2_test IS
   SIGNAL i_QSFP_RX : t_unb2_board_qsfp_bus_2arr(g_nof_qsfp_bus-1 DOWNTO 0); 
   SIGNAL i_RING_TX : t_unb2_board_ring_bus_2arr(g_nof_ring_bus-1 DOWNTO 0); 
   SIGNAL i_RING_RX : t_unb2_board_ring_bus_2arr(g_nof_ring_bus-1 DOWNTO 0); 
+  SIGNAL i_BCK_TX  : t_unb2_board_back_bus_2arr(g_nof_back_bus-1 DOWNTO 0); 
+  SIGNAL i_BCK_RX  : t_unb2_board_back_bus_2arr(g_nof_back_bus-1 DOWNTO 0); 
 
   SIGNAL serial_10G_tx_back_arr          : STD_LOGIC_VECTOR(g_nof_streams_back0+g_nof_streams_back1-1 DOWNTO 0) := (OTHERS=>'0');
   SIGNAL serial_10G_rx_back_arr          : STD_LOGIC_VECTOR(g_nof_streams_back0+g_nof_streams_back1-1 DOWNTO 0);
@@ -943,6 +945,15 @@ BEGIN
       i_serial_10G_rx_back1_arr(i) <= serial_10G_rx_back_arr(i+g_nof_streams_back0);
     END GENERATE;
 
+
+
+
+    i_BCK_RX(0) <= BCK_RX(g_nof_streams_back0-1 downto 0);
+    i_BCK_RX(1) <= BCK_RX(g_nof_streams_back0+g_nof_streams_back1-1 downto g_nof_streams_back0);
+    BCK_TX(g_nof_streams_back0-1 downto 0)                                       <= i_BCK_TX(0);
+    BCK_TX(g_nof_streams_back0+g_nof_streams_back1-1 downto g_nof_streams_back0) <= i_BCK_TX(1);
+
+
     u_back_io : ENTITY unb2_board_lib.unb2_board_back_io
     GENERIC MAP (
       g_nof_back_bus => g_nof_back_bus
@@ -953,10 +964,8 @@ BEGIN
 
       -- Serial I/O
       -- back transceivers
-      BCK_RX(0)  => BCK_RX(g_nof_streams_back0-1 downto 0),
-      BCK_TX(0)  => BCK_TX(g_nof_streams_back0-1 downto 0),
-      BCK_RX(1)  => BCK_RX(g_nof_streams_back0+g_nof_streams_back1-1 downto g_nof_streams_back0),
-      BCK_TX(1)  => BCK_TX(g_nof_streams_back0+g_nof_streams_back1-1 downto g_nof_streams_back0),
+      BCK_RX => i_BCK_RX,
+      BCK_TX => i_BCK_TX,
 
       BCK_SDA => BCK_SDA,
       BCK_SCL => BCK_SCL,
diff --git a/boards/uniboard2/designs/unb2_test/tb/vhdl/tb_unb2_test.vhd b/boards/uniboard2/designs/unb2_test/tb/vhdl/tb_unb2_test.vhd
index c9b9f289a0e6b84afbadb736b5ff997e9e37bf6e..fb138bea34134e9dc28412b80c2b84427499929b 100644
--- a/boards/uniboard2/designs/unb2_test/tb/vhdl/tb_unb2_test.vhd
+++ b/boards/uniboard2/designs/unb2_test/tb/vhdl/tb_unb2_test.vhd
@@ -114,6 +114,7 @@ ARCHITECTURE tb OF tb_unb2_test IS
   SIGNAL si_lpbk_6           : STD_LOGIC_VECTOR(c_unb2_board_tr_ring.bus_w-1 DOWNTO 0);
   SIGNAL si_lpbk_7           : STD_LOGIC_VECTOR(c_unb2_board_tr_ring.bus_w-1 DOWNTO 0);
 
+  SIGNAL si_lpbk_8           : STD_LOGIC_VECTOR(c_unb2_board_tr_back.bus_w-1 DOWNTO 0);
 
 
   -- Model I2C sensor slaves as on the UniBoard
@@ -200,26 +201,25 @@ BEGIN
 
       -- Serial I/O
       QSFP_0_TX  => si_lpbk_0,
-      QSFP_0_RX  => si_lpbk_0
- --     QSFP_1_TX  => si_lpbk_1,
- --     QSFP_1_RX  => si_lpbk_1,
- --     QSFP_2_TX  => si_lpbk_2,
- --     QSFP_2_RX  => si_lpbk_2,
- --     QSFP_3_TX  => si_lpbk_3,
- --     QSFP_3_RX  => si_lpbk_3,
---      QSFP_4_TX  => si_lpbk_4,
---      QSFP_4_RX  => si_lpbk_4,
---      QSFP_5_TX  => si_lpbk_5,
---      QSFP_5_RX  => si_lpbk_5,
-
---      RING_0_TX  => si_lpbk_6,
---      RING_0_RX  => si_lpbk_6,
---      RING_1_TX  => si_lpbk_7,
---      RING_1_RX  => si_lpbk_7
-
-
-      --BCK_TX  => si_lpbk_1,
-      --BCK_RX  => si_lpbk_1
+      QSFP_0_RX  => si_lpbk_0,
+      QSFP_1_TX  => si_lpbk_1,
+      QSFP_1_RX  => si_lpbk_1,
+      QSFP_2_TX  => si_lpbk_2,
+      QSFP_2_RX  => si_lpbk_2,
+      QSFP_3_TX  => si_lpbk_3,
+      QSFP_3_RX  => si_lpbk_3,
+      QSFP_4_TX  => si_lpbk_4,
+      QSFP_4_RX  => si_lpbk_4,
+      QSFP_5_TX  => si_lpbk_5,
+      QSFP_5_RX  => si_lpbk_5,
+
+      RING_0_TX  => si_lpbk_6,
+      RING_0_RX  => si_lpbk_6,
+      RING_1_TX  => si_lpbk_7,
+      RING_1_RX  => si_lpbk_7,
+
+      BCK_TX     => si_lpbk_8,
+      BCK_RX     => si_lpbk_8
     );
 
   ------------------------------------------------------------------------------