How to execute a 16 bit communication with a chip

[Sirmutt]

I have a thermometer chip which communicates via 16 bit read/writes.  The first 8 bits are a write of the address while the second 8 bits are a read (or write depending on address, but usually will be read after configuration).  The clock can be any speed I choose.  I have a 6251 DAQ, 6541 hi-speed DIO analyzer, 6602 counter, RS-232, and RS-485 modules in a PXI chassis. 

I'm not sure how to switch from write to read effectively (and in a timely enough fashion) to write the first 8 bits then read the last 8.  The delay in switching from a write to a read is too long if I use the DAQ to write a waveform then read a waveform on a digital channel. 

any ideas?

[gaving]

Hello SirMutt,

I'm sure that you can do this with the 6541, as it has per-line direction config.  I believe it uses the HSDIO driver, though.  You might find the section here down where it says "Interfacing with Digital Devices" helpful...

However, I don't have much experience with DIO, so I would suggest that you post to the Digital I/O forum here

http://forums.ni.com/ni/board?board.id=70

that way you can get the full benefit of the "community" since digital gurus will be monitoring these forums

Good luck!

-gaving

[Ryan_M]

SirMutt,

Are your communication channels bidirectional?  That is, are the 16 lines writting during some cycles then read on some other cycles?  The NI 655x is capable of per cycle tristates which allows for a hardware timed bidirectional interface.  If you don't need to switch directions in a hardware timed manner then the 654x that you have can issue a software command to tristate lines allowing for bidirectional, though this is not a hardware timed operation.  If then lines are split up, then the 654x can run independent generation and acquisition operations.  Using triggering, you can time them appropriately to your application. 

Check out some of the examples we ship with the NI HSDIO driver.  You should see a bunch of generation, acquisition, and simultaneous gen/acq examples that can get you started.