Complicated FPGA Problem

Thread Starter


Joined May 28, 2009
Good morning,
My name is Moraali. I am currently doing a project, but I have a problem on the cable communication issuefor more than 6 months.
FPGA is a Xilinx chip... You can get the info from
I am using Virtex4 ML401 (LX type)
The data sheet is on (look on the top left at sheet 12 )
So by using DMM, I found out that the PC and the Modem port is not loopback. Only the FPGA is loopback (pin 1,4and 6 is connected).
PC => Male Port
Modem => Female Port
FPGA => Male Port
I tested the cables (NOT the PC , NOT the MODEM , NOT the FPGA .... ONLY FROM THE CABLES USED) for three times and the result is below (for 9 Pin D Type ) :-
1) Presently what cable you are using in between PC and Modem? For your info, the flow control is none
PC Modem
2 => 2
3 => 3
5 => 5

2) And also what cable in between FPGA and PC?
2 => 3
3 => 2
5 => 5

3) I just tested between FPGA and Modem
FPGA Modem
2 => 2
3 => 3
5 => 5

I am not from engineering background. So, I am not so sure about labeling the Tx and Rx. I just assume that from the PC the 2 is Rx and the 3 is Tx. And 5 is definitely Gnd
a)Whether using any Hardware handshaking in between PC and Modem? - On both the 9 Pin D Type Connector check out the Pins
1- DCD
4 - DTR
6 - DSR
7 - RTS
8 - CTS
PC (Female) Modem (Male)
1 => 1
4 => 4
6 => 6
7 => 7
8 => 8
I only have you as my tutor. Please guide me. From the description ,
1)How can I rectify this problem? Should I buy a cable?
2)what type of cable should I purchase for the FPGA-Modem?
Please reply to me as soon as possible.
My contact:-
Thank you
Can you explain exactly what you mean by WORK FINE and DOES NOT WORK FINE? How are you testing each of these cases?

Have you written code for the FPGA to initiate communication with the modem?