PCIe-6536 Simultaneous Read and Write

Question

I have an application where I need to simultaneously read 24 bits (Ports 0-2) and write 8 bits (Port 3), using an external clock.  The way it is done now is I create a read task and I create a write task.  I send my external clock to PFI4 and PFI5, because two clock inputs are required (one for read, one for write).  And I send a trigger signal to PFI3 to start and synchronize the tasks.
However it is not working correctly.  My clock is ~15MHz and the reads and writes are off by a random number of a few clock cycles.  For example when I start writing out Port 3, the reading into Ports 0-2 will start 2 or 3 or 4 clock cycles later.  
Is there a way that I can read and write simultaneously that will work correctly??

Answer 1

I am still trying to figure out this problem.  I want to simultaneously write bytes out of Port_3  and acquire 24 bit words into Ports 0-2.  The only way I know to synchronize the tasks is to have them both start on a rising edge trigger signal on PFI3.
If my clock is a few hundred kilohertz, the tasks are synchonized.  When the clock is over 1 MHz then I start seeing the read of 24-bit words lagging the output write by 1 clock cycle sometimes.  The higher the clock rate, the more delay I see.  With a 20MHz clock I see a lag of 8 or 9 or 10 clock cycles.  I spent a lot of money on this card but it apparently doesn't work as advertised.  It is supposed to work up to 25MHz but I have problems at 1MHz.
The way I am testing it is to loop Port_3 directly into Port_2 with a short ribbon cable (using the CB-2162 test board made for the I/O card).  I can send a pattern out and read it in and see how many of the first bytes were not read in.  For some reason the Acquire task is lagging the Generate task...