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Ok for programming electronics I got myself an ftdi chip. I want to be able to invert the TX/RX/... signals so I can get some experiments working that I have on a paper.

To do this we have to re-program the device's eeprom.


read the eeprom

To read the EEPROM of the ftdi, use the software ftdi_eeprom.

  • download the software
wget http://www.intra2net.com/en/developer/libftdi/download/ftdi_eeprom-0.3.tar.gz
  • unpack it
tar xvzf ftdi_eeprom-0.3.tar.gz
cd ftdi_eeprom-0.3
  • build it
./configure && make -j4 && make install
  • find out your ftdi's serial ID:
hwinfo --usb
Serial ID: "A7006Ys2"
  • configure ftdi_eeprom to use your serial id:
sed -i "s/^serial=.*/serial=\"A9VQ459E\"/" example.conf 
  • read your chip's eeprom:
ftdi_eeprom --read-eeprom example.conf 
  • find the file name where the eeprom is stored in:
ls -ltr
-rw-r--r-- 1 root root   128 Dec 15 12:59 eeprom.new
  • verify that it is really an eeprom
# hexdump -C eeprom.new 
00000000  00 40 03 04 01 60 00 00  a0 2d 08 00 00 00 98 0a  |.@...`...-......|
00000010  a2 20 c2 12 23 10 05 00  0a 03 46 00 54 00 44 00  |. ..#.....F.T.D.|
00000020  49 00 20 03 46 00 54 00  32 00 33 00 32 00 52 00  |I. .F.T.2.3.2.R.|

Re-program the eeprom

To re-program the eeprom, better read it before and have a backup.

gcc -o write main.c -L/root/Downloads/release/build/x86_64/ -lftd2xx -lpthread -ldl -lrt -Wl,-rpath,/usr/local/lib
  • remove the ftdi_sio driver
modprobe -r ftdi_sio
  • disconnect all other FTDI chips
  • call the program to re-write the device's eeprom:

understand the eeprom's bits

Using the program ftdi_eeprom I can read the 128 bytes of user's eeprom from the FTDI RS232R chip. Using the "write" command compiled above I can change single values like InvertTXD in the eeprom. So let's set all Invert values to 0x00. The Invert values are:


Now I modify main.c so that all Invert values are 0x01, compile and run it and get eeprom-all1 via ftdi_eeprom. Then I modify main.c so that all Invert values are 0x00, compile and run it and get eeprom-all0 via ftdi_eeprom. Then I use the cmp to find out which values have changed:

# cmp -l eeprom-all0 eeprom-all1
 12   0 377
127 107 273
128 176 175

Indeed, byte 12 is 00h in eeprom-all0 and FFh in eeprom-all1. Besides, the last two bytes of the 128 bytes-file seem to contain a checksum, they are different as well.

See also