Problem with reading clocked 24 bit long words through VISA read.

[nagyo_g]

Hi!
Would like to read in 4 consecutive 24 bit long words, through the RX line of a COM port. The com line uses a clock besides the data, so I'm guessing they must be clocked, and probably means it is a synchronous rs232 communication. Still I just only need the bits of the 4 words. When I read in the data, and represent it with a string indicator, it just shows nothing (means empty string), but several bytes were read in, according to the bytes count (but in each run, I get different values). If I switch the indicator to hex mode, it shows 0s in different length. I already tried the proposed solutions in this article: http://digital.ni.com/public.nsf/allkb/6C24F2F07BC23BB78625722800710865, but still zeroes what I get. Unfortunately I don't know the baud rate of the communication, the things I know are: there are some additional leading bits, which are not important (the least significant 24 bits count), the clock frequency is 20 Mhz, and the clock and data pulse width is 25 ns too. Really don't have a clue, in which direction I should go, so I would really really really appreciate some help about this, because I have a due date on next tuesday. Thank you for any help in advance,
cheers 
nagyo

[JÞB]

The com line uses a clock besides the data, so I'm guessing they must be clocked, and probably means it is a synchronous rs232 communication

the clock frequency is 20 Mhz, and the clock and data pulse width is 25 ns

Ummm.... this does NOT sound like RS-232.  In RS-232 there are three ways to achieve syncronous data transfer (called clocking methods) but all of them depend on recieved data to recover the recieve clock.  Additionally, in practice it may be possible to excede 20Kb/sec with RS-232 however, this is rarely done.

What is the equipment connected on the other end?

[nagyo_g]

Well, maybe I used the term rs232 in a wrong way. I was just guessing about it. The equipment is a TRF6900EVM card, and I attached the important

parts from the manual, maybe that could help you understand the communication method!! Still waiting for the answer, why the VISA read function works that weird way I mentioned above.

[JÞB]

OK, what you have is an SPI interface.  You will not be able to use a RS-232 COM port without additional hardware. Period. EOM 

[JÞB]

Whoops, I miss spoke!  I need to RTFM  

• "The TRF6900 EVM board is used to evaluate the RF performance of the

TRF6900. It contains a PC parallel port interface"

• "P1 is the PC parallel port interface and is a male DB25 connector. P1 is

connected to the LPT1 or LPT2 port of the computer on which the
TRF6900 software is running."

[smercurio_fc]

It would be really nice if the poster STUCK TO ONE THREAD! 

http://forums.ni.com/t5/LabVIEW/method-of-serial-activity-logging/m-p/520433

http://forums.ni.com/t5/Instrument-Control-GPIB-Serial/Sniffing-a-probably-synchronous-serial-commun...