COTS solution for non-standard synchronous bi-directional serial interface?

[MGx]

NI Forum:

I am looking for a COTS solution for communicating with one of our heritage products having a non-standard synchronous bi-directional differential TTL serial interface as described below.  I am hoping that this is available as a PCIE (or similar) card. I am willing to have interface hardware that translates single-ended TTL from the host to differential TTL required by the product.

The product is normally in the “receive” mode awaiting a 27-bit serial command which consists of a start bit set to “1”, 25 bits of data, and a stop bit that can be set to either “1” or “0”.  Data is valid on the positive-going (positive logic) edge of a uni-directional differential TTL data clock provided by the host.  The product is specified for a maximum data rate of 50 KBPS (set by the host’s data clock).

After a valid serial command is received, the product responds by changing to the “transmit” mode within a few data clock cycles.  For all but one command, the product then synchronously echoes the 27-bit command that was received, except that the echoed data is valid on the negative-going edge of the (host’s) data clock and the stop bit is always set to a “1”.  For the “Block Read EEPROM” command only, the product responds by transmitting a serial string of about 1300 bits of data, also formatted as a series of 27 bit words.  The product does not provide a bit showing the direction of the data flow, so the host must be able to determine when to send or receive without a handshake from the product.

I am willing to consider “bit banging” a parallel port to produce the required serial interface using some of its outputs if this offers an advantage in providing for the 27-bit word format.  Also, I am willing to capture the Block Read EEPROM data as a single array and then figure out how to extract the data from the 27-bit word format.

I would appreciate any guidance on this matter, with one warning: my background is mostly in analog hardware, so I might not catch all of the lingo.  You may have to speak slowly.

Regards,

MGx

[jallen88]

MGx,
Are you looking for recommendation on a hardware device to use? Or are you simply looking for examples of LabVIEW code that will help you achieve this?

This sounds very similar to serial or GPIB communication, is it one of these two?

[MGx]

Jared A.

Thanks for your attention.  I am mainly looking for a hardware recommendation.  My chief (and probably un-informed) concern is that from what I have been reading, serial communication between a PC and another device generally involves asynchronous serial data that is sent and received in byte-sized packages each having a start bit and a stop bit.  I was hoping to be able to buy a PC-based COTS device that allows me to talk and listen directly to our product in its own 27-bit serial format without other intervening hardware.  Is there COTS hardware (and associated drivers) that can do this? Or must I also buy or design some sort of format translation circuit that decodes a standard serial format from a PCIE or GPIB card and relays the 27-bit serial words to and from my product?

Thanks for your help,

MGx

[jallen88]

MGx,
Thank you for your reply. After hearing more about your system, it seems that your application will require a custom solution. Unfortunately, National Instruments does not specialize in off-the-shelf solutions.

However, we do offer a number of Serial and Digital I/O cards that will aid you in building a device that will let you talk and listen to your product. I believe you should look at the following products we offer. I hope that these will help you in building your own custom solution:

Digital I/O: http://www.ni.com/digitalio/

Serial Interfaces: http://www.ni.com/serial/