Hello Siddu,
There are two groups of timing/handshaking lines on your PCI-6533, so at most
you can do two simultaneous operations. Because these timing signals need
to be divided up between your ports, there are only certain combinations of
ports you can use when configuring two operations to take place
simultaneously. If you are performing two 8-bit read or write operations,
the divide up of these timing signals dictates that you must perform these
two operations on ports 0 and 2. If you are performing two 16-bit
operations, the first operation must combine ports 0 and 1, while the second
operation must combine ports 2 and 3. Because of the limit on the number
of lines, you can only perform one 32-bit operation, which will only use one
set of timing/handshaking lines and ports 0,1,2, and 3. So, if you want
to perform two operations, one involving port 1 and the other involving port 3,
the only way to do it is to do 16-bit operations and ignore the data being
read/written to ports 0 and 2.
This separation of timing duties should not affect the performance of your
card, but for future reference, the PCI-6533 only has a 16 word FIFO (onboard
buffer), so your application it is actually quickly transferring data to and
from your PC's system memory (RAM). The PCI-6534 comes with two 32 MB
onboard memory buffers for applications that demand transfer rates of over 20
MHz.
I hope this is clear and let me know if you have any further questions.
Regards,
Travis G.
