Need RS 422 Function Generator and RS 422 SDLC coomunication

[Kim]

I am working on a project that require a clock that is RS 422 eletric spec at 500Khz and also at the same time, can send command to the test unit using RS 422 SDLC. It can be from 2 different cards. Did anyone know any hardware that can generate RS 422 signal at that speed. Any hardware can send RS 422 SDLC command. We have PXI 8433/4 but that will not work. Can use one of the port to generate the clock signal but can't send SDLC command.

thanks.

[Ben]

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Kim wrote:

I am working on a project that require a clock that is RS 422 eletric spec at 500Khz and also at the same time, can send command to the test unit using RS 422 SDLC. It can be from 2 different cards. Did anyone know any hardware that can generate RS 422 signal at that speed. Any hardware can send RS 422 SDLC command. We have PXI 8433/4 but that will not work. Can use one of the port to generate the clock signal but can't send SDLC command.

thanks.

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THe last time I did a high-speed SDLC app I used a-PCI from Fastcom

www.commtech-fastcom.com

I was able to do (?) 2 MHz using that device.

I just looked again and they are now pushing 12MHz!

Since then I have noticed that companies like Black Box are offering higher speed protocol converters so if Black Box has something on the shelf...

Ben

Message Edited by Ben on 05-13-2010 02:15 PM

[Kim]

Thank you very much Ben.

I will look into that.

[slbLV]

If you would consider external hardware,

the MAXIM  MAX1480 IC family works real fine for 422/TTL interfacing,

plus includes Isolation across the interface...

http://www.chipcatalog.com/Maxim/MAX1480A.htm 

(I kind of believe you are after an on-board solution though) ??

[Kim]

Thank you very much slbLV.

Not sure RS 422/TTL will work for us. Not familiar  with 422/TTL. Need more research for that.

The test unit also require a external clock that operate at 500kHz (+-10kHz) with amplitude from -6V to 6V (RS 422 eletric spec).  Our function generator can only generate signal with amplitude 0 to 5V. Thought about using digital IO going through programmable power supply except it only work on low frequency.

Anyway, thanks for all the input.

[slbLV]

The MAXIM IC is a TTL to RS-422  and a RS-422 to TTL  converter (bi-directional).

It will privide the RS-422 signals you need.

[Ben]

One thing you do pick-up using the Off-The-Shelf stuff I mentioned is "Bit-stuffing". 

In SDLC the data is self-clocked so the clock signal is derived from the signal line. THe clock syncronization requires regular re-syncing via a "sync-byte". SInce there is a potential that the data could be carying data that is the same as the "sync-byte" the SDLC protocl dictates that the sync-byte can never be transmitted in the data packet so "Bit-stuffing" is used where extra bits are inserted to prevent false sync-bytes.

Bit-stuffing requires manipulating the data going out and processing on the way in.

I spent some time working on fast LabVIEW code that would implement bit-stuffing. At the time I was working with 400 MHz PC. In my case I had to handle 8 channels at 2 MHz so PC's from that era simply could not keep up with all of the work for 8 ports.

So the OTS is worth concidering.

THe other bonus I picked from the Comm-Tech approach was they exposed functions that let me atack the physical layer for testing (inserting errors).

And of course there is another idea...

FPGA can be clocked at 40MHz so with the chip mentioned above, you could code up your own SDLC interface using FPGAs.

So have fun and please post back to let us know how you decide to proceed. It will help others that follow in your foot steps.

Thank you,

Ben  

[Kim]

Thanks for all the help.

Look like I am taking something more than I can handle. No realize what I get myself into. That will be a good learning experience.

I am hoping I can buy some 'ready' product that will handle the SDLC protocal for me and I just send the command to the test unit, uisng Labview VISA. Look like it is more than that. Using the PXI 8344/4, I manage to generate the clock by using a very large string (length of more than 1000000). Unfortunely, I can only use one port at a time, can send the clock signal but can't using the other port for command simutaneously.

We are thinking about using the PXI8344/4 for clock generation and General Standards Corporation PCI-SIO8BXS for the SDLC communication. Hope this will work !!!

Again, thank you very much for all the input and help. I appreciate that.

[Spectre_Dave]

Kim

This may help if you want to use a RIO like  Ben mentioned.

HDLC

[Ben]

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Spectre Dave wrote:

Kim

This may help if you want to use a RIO like  Ben mentioned.

HDLC

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Thank you for that link Dave!

It is nice to know my suggestion is sound.

I did not look at that code, but there is a top end baud rate limited in the clock rate of the cRIO so think about that before commiting.

Ben

PS: love the gun-ship avatar!

Message Edited by Ben on 05-14-2010 09:23 AM