Experimental Physics and
Industrial Control System

Hi EPICS users,

This is a very basic question regarding getting started with binary inputs, and the purpose of RVAL. (As an aside, perhaps we should anyone provide an example for a binary input (bi) similar to the “temperature:water” (ai) example from the Getting Started guide under “Test EPICS”, at:

https://docs.epics-controls.org/projects/how-tos/en/latest/getting-started/installation.html#test-epics

My students and I have been struggling to get a simple binary input working, though I think we’ve got it now. We first tried expanding, in the above Getting Started tutorial, the “test.db” script with:

test.db:

“””

record(ai, "temperature:water")

{

    field(DESC, "Water temperature in the fish tank")

}

record(bi, "isfishy")

{

    field(DESC, "True if the fish tank has fish inside.")

}

“””

However, “caget isfishy” shows a blank value, and “caput isfishy 0” does not seem to change anything. This perplexed us for a while.

Looking into it further in the user docs, we landed at documentation for the binary input record: https://epics.anl.gov/EpicsDocumentation/AppDevManuals/RecordRef/Recordref-11.html

Then, we tried modifying ZNAM and ONAM such as

test.db:

“””

record(bi, "isfishy")

{

    field(DESC, "True if the fish tank has fish inside.")

    field(ZNAM, "False")

    field(ONAM, "True")

}

“””

And now we can do “caput isfishy 1” and all “caget isfishy” prints with “True”, as does “caget isfishy.VAL”. However, I noticed that “caget isfishy.RVAL” still gives 0. So here’s my question: Is this zero in RVAL expected even though the Boolean is now True, and why? Thanks!

Scott