RE: BO which should switch to 1 whenever processed

["Pearson, Matthew via Tech-talk" <tech-talk at aps.anl.gov>]

Hi,

 

You may have to have that extra record, although there’s usually a few ways of doing this.

 

In the bo record documentation it says:

 

If closed_loop is specified, the VAL field’s value is obtained from the address specified in the Desired Output Link (DOL) field which can be a database link or a channel access link, but not a constant.

 

The HIGH field function will set VAL back to 0, so after the first processing you’re writing 0 each time instead of 1, unless you have that second record writing a new 1 each time.

 

It might make it easier to digest by renaming the record ‘Go’ (or similar), instead of ‘Constant’, and use another bo instead of longout, like:

 

record(bo, “Go”) {

  field(VAL, “1”)

  field(OUT, “MoveToPos PP”)

}

record(bo, “MoveToPos”) {

  field(OUT, “$(MOVE_OUTLINK) PP”)

  field(HIGH, “1”)

}

 

Or, you could incorporate a seq record to write the position and trigger the move:

 

record(seq, “MoveToPos”) {

  field(DLY0, “0”)

  field(DOL0, “SelectAbsPos”)

  field(LNK0, “$(POS_OUTLINK) PP”)

  field(DLY1, “0”)

  field(DOL1, “1”)

  field(LNK1, “$(MOVE_OUTLINK) PP”)

  field(DLY2, “1”)

  field(DOL2, “0”)

  field(LNK2, “$(MOVE_OUTLINK) PP”)

}

 

Also, this FLNK line:

field(FLNK, "MoveToPos PP")

doesn’t need the PP link attribute.

 

Cheers,

Matt

 

 

record(longout, "Constant1") {

    field(VAL,  "1")

    field(OUT,  "MoveToPos PP")

}

 

record(bo, "MoveToPos") {

    field(HIGH, "1")

}

 

 

 

 

From: Tech-talk <tech-talk-bounces at aps.anl.gov> On Behalf Of Majer Karel via Tech-talk
Sent: Thursday, April 23, 2026 3:45 AM
To: tech-talk at aps.anl.gov
Subject: [EXTERNAL] BO which should switch to 1 whenever processed

 

Hello, I would like to have a BO record which sets its value to 1 whenever processed (without necessarily writing 1 to VAL), then back to 0. It's part of PLC-based motion control IOC. The database should allow moving the motor to saved waypoint

Hello,

 

I would like to have a BO record which sets its value to 1 whenever processed (without necessarily writing 1 to VAL), then back to 0.

It's part of PLC-based motion control IOC. The database should allow moving the motor to saved waypoint positions; it looks like this:

 

record(ao, "AbsPos") {

    field(EGU,  "step")

}

 

record(ao, "Waypoint1") {

    field(EGU,  "step")

}

 

record(longout, "WaypointIdx") {

    field(FLNK, "SelectAbsPos")

}

 

record(sel, "SelectAbsPos") {

    field(SELM, "Specified")

    field(NVL,  "WaypointIdx")

    field(INPA, "AbsPos")

    field(INPB, "Waypoint1")

    field(FLNK, "DesiredPos")

}

 

record(ao, "DesiredPos") {

    field(EGU,  "step")

    # field(OUT,  "OUTLINK")  link to PLC

    field(DOL,  "SelectAbsPos")

    field(OMSL, "closed_loop")

    field(FLNK, "MoveToPos PP")

}

 

The processing chain is WaypointIdx -> SelectAbsPos -> DesiredPos -> MoveToPos

MoveToPos is a BO which tells the PLC to start motion, and it must have HIGH field set to non-zero. I'm having a problem triggering its processing in a way that its value becomes 1.

I tried this:

 

Record(bo, "MoveToPos) {

    # field(OUT,  "OUTLINK")  link to PLC

    field(DOL,  "1")

    field(OMSL, "closed_loop")

    field(HIGH, "1)

}

 

I expected that processing the record would set VAL to 1, then back to 0 after 1 second. It works only once; subsequent processing does not switch value back to 1. Writing 1 into VAL works as expected. Is this the correct functionality of the BO record?

 

I ended up with the following construct, which provides the desired functionality, but I don't much like having a record which only holds a constant value to be put into the BO. Is there a better way to do this?

 

record(ao, "DesiredPos") {

    field(EGU,  "step")

    # field(OUT,  "OUTLINK")

    field(DOL,  "SelectAbsPos")

    field(OMSL, "closed_loop")

    field(FLNK, "Constant1")

}

 

record(longout, "Constant1") {

    field(VAL,  "1")

    field(OUT,  "MoveToPos PP")

}

 

record(bo, "MoveToPos") {

    field(HIGH, "1")

}

 

Thanks,

 

Karel

 

 

 

Karel Majer | Senior software developer
Phone: +420 266 051 514
E-mail: karel.majer at eli-beams.eu

ELI Beamlines Facility|The Extreme Light Infrastructure ERIC Za Radnicí 835, 252 41 Dolní Břežany, The Czech Republic www.eli-beams.eu