how to programm inidividual bits in a byte frame

[Sergoreg]

Hi,

I was wondering if it's possible or how to program individual bits in a frame
NI PCI-8431/4 board.

I don't want to use standard serial port frame format with stop-start-parity bits,
but would like an option to prepare a frame in advance so the board will emit at specified time.

On a slow speed it's possible to do it using 'break' signal and rely on PC timer but on
higher bitrates it's difficult.

I'm not familiar with NI-VISA, maybe it allows this.

Best regards,
Sergo.

[pflores]

Sergo,

What are you trying to communicate with/control with this port? NI-VISA allows you to configure the frame within normal Serial settings, but not much more than that. Also, to send out a frame at a specific time, you would just poll the system clock then have a VISA write. this will probably give a latency in the ms or 10's ms range, depending on your cpu speed, processor usage, etc.

If you share what you are trying to do, maybe we can find a more approproate solution.

Thanks!

[Sergoreg]

Hi Peter

I need to simulate a serial interface but it's not standard encoding, so I would like an option to prepare a byte array of in buffer and emit it at specified time.
And there is no stop or parity bits, only start.
It would be good if I could transmit clock signal, and start of transmission signals on other channels.
Preprogram all of it on a card a make it do it at specified time.
S.

[pflores]

I do not know of any RS232 boards that will give you this finctionality as it breaks the specificationfor the communication standard. What are you trying to communicate with?

Your bet bet may be to look at a digital IO board. These will allow you to specify a custom bit string as long as you want without introduction of any overhead characters like start, stop, or parity bits. Here is a list of allour products with digital output functionality. Most have a 5V "high" value, some have up to 60V. They all have a 0V value for a "low".

If these voltage values do not work for what you need, you can look at analog output which typically has a range of +/- 10V, but can go higher.

Does this help? Feel free to share more details about your application or contact customer support via ni.com/support