Setting time critical digital output based on axis position (PCI-7358)

[Martin.D]

HI,

I need to set a time critical digital output based on encoder position (this will switch fast acting valves). I was planning to try the general purpose DIO but I can't find any examples, I have been through the manuals, searched the site etc. Where can I find help with this, all the examples only seem to deal with digital input triggering or RTSI? I'm thinking of an onboard program that just monitors encoder positions and sets digital outputs.

Some time back I seem to remember reading that general purpose DIO should not be used for time critical operations, is that correct? And if so what are the other options - RTSI going to another DIO board? The DIO really needs to be deterministic, is RTSI the only option?

Any advice appreciated / Martin

[Jochen]

Even with an onboard program you will always get a delay of several milliseconds between your axis has crossed the position and until the digital outputs are set. If this is ok for you then you could choose this approach.

For the case that you only want to toggle one digital line the Breakpoint feature should be the best solution as it toggles the breakpoint output almost immediately when the breakpoint positions are reached.

If you need to change a whole pattern instead of only a single line then the approach you mentioned would be the best solution (RTSI and high-speed DIO like the 653x boards). Combine this approach with the breakpoint feature by routing the breakpoint output to RTSI and using this as a update clock signal for the DIO board.

Best regards,

Jochen Klier
National Instruments Germany

[Martin.D]

Thanks Jochen,

I can use breakpoints because I only have one time critical digital output required per axis. I was incorrectly trying to configure a general purpose DIO to a breakpoint - this is not possible I think. So thanks for the help.

Martin