Compact FLash UDMA Mode Problem

Hello,

I'm designing a board with EP2S30 and a compact flash as a compact flash reader board.

FPGA drives the Compact Flash pins. Pins are set as LVCMOS and weak pull ups enabled in data pins.

In memory mode or True IDE mode there is not any problem while accessing Compact Flash.

Also In True IDE Mode Multiword DMA cae there is not any problem.

However while writing data to Compact Flash in True IDE Ultra DMA mode. I have no problem in reading from CF in True IDE Ultra DMA Mode.

The problem is that :

When executing DMA Write command in True IDE Ultra DMA Mode, while IORDn(HSTROBE) is low, FPGA drives the CF data pins Data(15:0) and voltage level of data pins decreases.I'm supplying CF with 3.3 Volts. About 0.5V decrease occurs in data pins through a series resistor which means there is about 20~30mA current in each data pin. When HSTROBE is high there is not any decrease in voltage level of data pins. And there is not any decrease in the supply voltage of Compact Flash in any case.

There is scope view of the case as attachment.

I do not understand why a decrease occurs in voltage level of data pins. And why CF sinks too much current from its data pins when there is no voltage decrease in power pins.

Is there anybody that encounter with a same problem?

Thank you so much for your help.