Ftdi

Ok for programming electronics I got myself an ftdi chip buying this package. Now want to be able to invert the TX/RX/... signals so I can get some experiments working that I have in this book.

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.

• download the ftd2xx library http://www.ftdichip.com/Drivers/D2XX.htm
• download http://svn.icmb.utexas.edu/svn/repository/trunk/zpub/sdkpub/usbkey_dlpd/macosx/d2xx/Samples/EEPROM/write/main.c
• compile it using

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:

./write

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:

InvertTXD 
InvertRXD
InvertRTS 
InvertCTS 
InvertDTR 
InvertDSR 
InvertDCD 
InvertRI

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

• http://svn.icmb.utexas.edu/svn/repository/trunk/zpub/sdkpub/usbkey_dlpd/macosx/d2xx/Samples/EEPROM/write/main.c
• http://www.ftdichip.com/Support/Documents/ProgramGuides/D2XX_Programmer%27s_Guide%28FT_000071%29.pdf - good overview what the bytes in the EEPROM mean.