Each connected board have power problem

[u24c02]

Hi
i have problem that it's seem like power.
*
When i working fx2lp board and fpga board.
So i connect with both board *for slave fifo working.
Fx2lp board is just connected USB cable( it's just use power from usb cable).
*
When i connect FPGA Board to Fx2lp board, FPGA Board's led is weak on.
it's seem like something wrong. but slave fifo is working well(stream project ).
*
I dont know what am i check ?
*
*if i use 16bit slavefifo mode, which pin used for i2c in fx2lp-56pin?
how can i handle of this problem?

 

[wp100]

Hi,

I assume you are also connecting power to the second board , not just the data signal connections ?

Is the USB cable from a desktop pc or laptop ? - there is a limit as to how much power a usb cable can supply.

I am not familiar with those boards, but if you have a test meter you need to measure the voltage and current to each board when connected separately, then with both boards connected together.

It sounds like you either have a short circuit on one board or the total power needs exceed the usb cable.