Hello All,

I have an application that is currently using FTDI USB to serial converter for communication between PC and Controller @ a baudrate of 250kbps with a TTL level output.

We are finding that while we need to transmit between 10-15 bytes of data, the USB frame size is much larger (4kb?) and consequently we are encountering a delay - a lag in processing. (we assume this is the reason for the delayed communication - any experience here would be enlightening)

We are looking for an alternative means of interfacing with the PC through a PCI to Serial communication card. Considering the existing built components, such a card must operate at the 250kb baud at TTL voltage levels.

Do let me know if there is a suggestion on what card can be used for this application.

 

Your bit rate is kind strange. Do you mean 256000 bits per second that is more common?

 

No, the bit rate is 250000 bits per second

The existing controller communication is operating at 250000 bits per second and we are looking forward to retain it, so as to avoid any changes in the existing control system.

 

One solution is to find a serial comm card and set it to the desired baud.
Bypass the RS-232 transceivers and go direct TTL.

 

Look at the products that FTDI have and tell us exactly which cable you have so it is easier to reverse engineer.
http://www.ftdichip.com/Products/Cables/USBTTLSerial.htm

 

Hello All,

Thank you for your interest.


MrChips,

For the Serial comm cards that we have come across, 115200 bits per second is the maximum baudrate that can be achieved. In our case the requirement is 250000 bits per second. Please suggest me one, if you have come across.
If we can find such a comm card then we can think for further development.

LDC3,

We are using FTDI FT232R device for making the cable, using the demo circuit provided by FTDI.

 

First thing, I had no problem running and FTDI chip at 312,500 baud, but this was a bulk transfer with no control characters, so the delay didn´t matter.

One thing that comes to my mind, how cpu extensive is the reply from the PC? I mean could you send it to another microcontroller and buffer the data there, then send to pc for example through normal usb?
Or what kind of communication is actually going on over the serial link?

 

And anyway, just a simple search for sata rs232 gave mi this link: http://www.brainboxes.com/product/items/px-846 which is a sata card capable of up to 921,600 baud. You´d have tosak them if it works on non-standard rates like your´s.

 

Looking into your problem yesterday. I found with a quick search on Google several high speed serial cards many based on the 16950 UART. http://www.google.com/search?q=high+speed+pci+express+serial+card How ever they all seams to have RS232 level converter as frontend. Your problem may also be that any Windows systems are not realtime systems and hence not deterministic(which is a better for for real time). It will always be some delay as the data find the way to your GUI.

 

Thank you All,
For your feedback throughout.

Kubeek,

For your earlier reply ::
"One thing that comes to my mind, how cpu extensive is the reply from the PC? I mean could you send it to another microcontroller and buffer the data there, then send to pc for example through normal usb?
Or what kind of communication is actually going on over the serial link? "

The Communication is for a typical Motion control system and the application demands a real time basis communication. And as far as sending it to another microcontroller is concerned, that means a considerable amount of development work(which we are trying to avoid if possible) at the controller end. Thus a PCIe to serial communication is a favourable solution, as we only need to add a card inside the computer and make the necessary software changes.
We were able to find a suitable card for our requirements @ http://www.banggood.com/Wholesale-P...erial-Card-Mos-Chip-MCS9922-Chip-p-63368.html

Still further we need to convert the Serial comm signals to +5V TTL, for which we have found MAX3243CDW line driver. For the moment we seem to have the required hardware for our solution. Wish us all the best. Thank you.