Experimental Physics and
Industrial Control System

Ned Arnold <nda> · Thu, 7 Nov 2002 11:15:21 -0600 (CST)

This has come up often ...

The MBBO record is limited to 16 values because all
enumerated values passed by channel access are limited 
to 16 states (MAX_ENUM_STATES). If this is changed, everything
breaks.

There aren't any "perfect" work arounds. Here are two I have 
seen used:

1) If you want strings on a menu, define multiple MBBO's to 
   cover as many as you need. A unique value can be calculated
   in the database depending on which MBBO changed. Unfortunately, 
   all clients that want to use these PVs will have to decide which 
   PV to write to. 

   For an operator GUI, a TCL/TK application can be written that 
   provides ALL menu choices and writes to the appropriate PV.

2) If you can do without strings, use a longout record that can
   then fanout to calc records and mbbo's to determine the
   appropriate action.

   	Ned

> 
> 
> I have a device where I need to select 1 of 22 inputs.  The logical record
> choice is MBBO, but it is limited to 16 values.  Is there a way to chain
> together 2 MBBO records to get more than 16 choices?  Any reason that MBBO
> was limited to 16 values, rather than 32?
> 
> Thanks,
> Mark Rivers
> 

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System