TDC communication with PC ?

Hi every one ,  I have a problem about communication.

My system is like that:

1  One TDC rack with two CPU  and to CP moudle。  CP51M1 Ethernet 。

2   One PC with  windows XP SP3 OS .  

3  PC Install Visual Stuodio 6.0 with SP6 

4   I have make a project in VB6   and create link between TDC and the PC software.

The software use WinScok control.

5   In my software  i can recieve data from TDC , but TDC can not recive data form PC.

6   Can anybody give some help to do this communication commission.

New question published by lileishihaoren is split to a separate thread with the subject Small dll which can read or write data directly.

Best regards
Jen_Moderator