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                8.1     PRESENT SOFTWARE . . . . . . . . . . . . . . . . . 8-1
                8.2     PROPOSED MODIFICATIONS . . . . . . . . . . . . . . 8-3
                8.3     PROBLEMS AND COMMENTS  . . . . . . . . . . . . . . 8-5

                                      CHAPTER 8
                     SOFTWARE TO CONTROL GENERALIZED ANALOG KNOBS
        The SLC system will need a facility to control a number  of  different
        analog  devices using a Transiac DAC channel to output a voltage and a
        SAM channel to monitor the setting.  In general,  these  devices  look
        like magnets with the following exceptions:
              o  They do not need to be calibrated, and should not be.
              o  They are not standardized.
              o  When trimmed, the DAC should be set but no attempt should  be
                 made to improve the setting by iteration.
        Since the necessary functions are properly  a  subset  of  the  magnet
        control  functions,  it  will  be  possible to use the existing magnet
        control software to control these  analog  channels  with  only  minor
        modifications.

        8.1  PRESENT SOFTWARE

        In the present  magnet  control  software,  there  are  five  possible
        control functions:



        SOFTWARE TO CONTROL GENERALIZED ANALOG KNOBS                  Page 8-2

              o  CALIBRATE
                 The Calibrate function sets the DAC to specified high and low
                 values and recalculates a linear fit to the DAC vs I transfer
                 function.
              o  CHECK
                 The Check function reads  the  appropriate  SAM  channel  and
                 calculates  the  present  value of current and B field, BACT.
                 It then compares BACT with the desired field, BDES, and  sets
                 status bits to indicate if the reading is within tolerance.
              o  PERTURB
                 The  Perturb  function  sets  a  new   value   of   BDES   by
                 extrapolating  from  the  present  DAC  setting.  There is no
                 readback or checking.
              o  TRIM
                 The Trim function takes the desired field,  BDES,  calculates
                 the appropriate DAC setting, and sets the DAC.  It then reads
                 back the field, BACT, compares it with BDES, and iterates  up
                 to  10  times  with  new  DAC  settings  to  get  BDES within
                 tolerance of BACT.
              o  STANDARDIZE
                 The Standardize function cycles the magnet from full high  to
                 full  low  current  a  specified  number  of  times, NSCY, to
                 reproduce the cycle used by the magnetic  measurements  group
                 to  give  the  magnet amnesia.  If NSCY is 0, a magnet is not



        SOFTWARE TO CONTROL GENERALIZED ANALOG KNOBS                  Page 8-3

                 standardized.
        The present software requires a magnet to be calibrated before it  can
        be  Perturbed, Trimmed, or Standardized as all three functions use the
        DAC vs I transfer function from the calibration to  calculate  desired
        DAC settings.
        The present software has reserved two hardware status, HSTA,  bits  to
        indicate  that  a  magnet  is not capable of full control.  These bits
        are:
              o  HSTA_NOCTRL to indicate that the magnet can be read  but  not
                 controlled.   If  this bit is set, all functions except Check
                 are disabled.
              o  HSTA_NOTRIM to indicate that the magnet can be controlled but
                 not trimmed independently.  This has been used in cases where
                 multiple magnets share a common DAC and ADC channel.  If this
                 bit is set, the Trim function is disabled.

        8.2  PROPOSED MODIFICATIONS

        The new devices may be controlled using the existing routines  in  the
        Micros and the existing control routines in the VAX.  They can use the
        existing magnet displays, but they will not be included when  the  ALL
        magnet button is selected.



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        It is suggested that the 2 HSTA bits currently in use be expanded to 4
        disable bits, one for each actual control function.
              o  HSTA_NOCALB to indicate that calibrate is disabled  for  this
                 device
              o  HSTA_NOPTRB to indicate that perturb  is  disabled  for  this
                 device
              o  HSTA_NOTRIM to indicate that trim is disabled for this device
              o  HSTA_NOSTDZ to indicate that standardize is disabled for this
                 device
        In addition, one extra bit is needed to indicate that the  device  can
        be  trimmed,  but that no attempt should be made to iterate to improve
        the setting.
              o  HSTA_NORETRY to indicate no iterations on trim
        The standard bit configurations would then be as follows:
              o  NO BITS SET for normal magnets with full control available.
              o  HSTA_NOCALB+HSTA_NOPTRB+HSTA_NOTRIM+HSTA_NOSTDZ   for   extra
                 magnets sharing a single DAC and ADC channel.
              o  HSTA_NOCALB  for  malfunctioning  magnets  which   will   not
                 calibrate  but  are  still  needed by the system in a limited
                 capacity.



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              o  HSTA_NOCALB+HSTA_NOSTDZ+HSTA_NORETRY  for  the   new   analog
                 devices.
        It is also necessary, to allow devices with the HSTA_NOCALB bit on  to
        be perturbed, trimmed or standardized using the test DAC vs I transfer
        function instead of the calibrated transfer function.

        8.3  PROBLEMS AND COMMENTS

        Problem:  These devices will be grouped under a new  database  Primary
        name   or  names,  e.g.   :PHAS:.   As  the  present  set  of  primary
        definitions have used all the available primary definition space,  the
        database will need to be modified before these devices can be defined.
        Problem:  After the addition of the  5  bits  described  above,  there
        remain  only  2  unassigned bits in the Hardware status word.  This is
        not much growing room.
        Comment:  For present applications, the HSTA_NOSTDZ bit is unnecessary
        as magnets which should not be standardized have the number of cycles,
        NSCY, set to 0.  In addition, HSTA_NOTRIM and HSTA_NOPTRB are probably
        redundant and could be combined.  This may be necessary if more status
        bits are needed.
        Comment:  Since the HSTA word is in  the  database  supertype  2,  and
        hence  modifiable  by the VAX, software could be written to turn these
        bits ON and OFF dynamically.  This may be more dangerous than useful.



        SOFTWARE TO CONTROL GENERALIZED ANALOG KNOBS                  Page 8-6

        Problem:  Since the  new  devices  will  be  controlled  by  the  same
        routines  in  the  micros  as the magnets, there is a possible problem
        arising from the fact that all devices with the Trim command  bit  set
        will  be  Trimmed  whenever  the  magnets  in that sector are Trimmed.
        Other functions will not be used, except check and perturb,  and  will
        not be likely to cause problems.
        Comment:  Care will have to be taken to define tight  Trim  tolerances
        and  loose  Check  tolerances for the new devices so that they will be
        trimmed whenever their BDES is changed but they will  not  fail  Check
        due to the inaccuracy of the readback.