Document the magic 0x02 0x03 0x01 value after the serial string

diff --git a/doc/EEPROM-structure b/doc/EEPROM-structure
index 09c3e45..97fd6d0 100644 (file)
--- a/doc/EEPROM-structure
+++ b/doc/EEPROM-structure
@@ -92,6 +92,15 @@ CHIP values:
 
 1a        UA (all)
 
-Mprog doesn's seem to write this:
-After last string
-0x02 0x03 0x01 with PnP == 0
+
+Additional fields after the serial string:
+One byte: 0 - reserved for "legacy port name prefix"
+One byte: 0 - reserved for "legacy port name prefix"
+One byte: 0 - reserved for plug and play options
+(Observed values with PnP == 0:
+0x02 0x03 0x01)
+
+Note: The additional fields after the serial number string
+collide with the official FTDI formula from AN_121 regarding
+the start of the user area:
+"Start Address = the address following the last byte of SerialNumber string."