diff --git a/libraries/io/eth/src/vhdl/eth_statistics.vhd b/libraries/io/eth/src/vhdl/eth_statistics.vhd
index 51f22e7599a06695851e159e4e8f2bc0ed93a5bb..0fb1ce71315a0b2a1b3ce41625f52e8b7f964ce4 100644
--- a/libraries/io/eth/src/vhdl/eth_statistics.vhd
+++ b/libraries/io/eth/src/vhdl/eth_statistics.vhd
@@ -35,6 +35,8 @@
 --   simulation delta cycle.
 -- . The eth_serial_in becomes active /= '0' when the Tx Eth is actually
 --   sending data, so this depends on the application or tb stimuli.
+-- . The transceiver sim model use 'U' to signal eop in tx_serial_out, so
+--   this is why then 'red' signal level appears in Wave window.
 
 LIBRARY IEEE, common_lib, work, technology_lib, dp_lib, tech_tse_lib;
 USE IEEE.STD_LOGIC_1164.ALL;