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                50.1    GENERAL DESCRIPTION  . . . . . . . . . . . . . .  50-1
                50.2    CONSTRUCTION . . . . . . . . . . . . . . . . . .  50-1
                50.3    LOGIC DECODER CARD.  . . . . . . . . . . . . . .  50-1
                50.4    STEPPING MOTOR DRIVER CARD.  . . . . . . . . . .  50-1
                50.5    MOTHER-BOARD.  . . . . . . . . . . . . . . . . .  50-2
                50.5.1    Backplane Connector Pinouts: . . . . . . . . .  50-2
                50.6    POWER SUPPLIES.  . . . . . . . . . . . . . . . .  50-3
                50.7    DRAWING PACKAGE NUMBER . . . . . . . . . . . . .  50-3
                50.8    RESPONSIBLE ENGINEER . . . . . . . . . . . . . .  50-3

                                      CHAPTER 50
                          STEPPING MOTOR DRIVER CRATE (SMDC)

        50.1  GENERAL DESCRIPTION

        The SMDC is a crate which is used,  in  conjunction  with  the  Moving
        Magnet Controller (MMC), to drive the stepping motors used to move the
        position of the magnets in the SLC arcs.  Each stepping motor drives a
        cam  that  moves one end of a magnet.  A potentiometer is connected to
        the cam shaft to indicate position, the  potentiometer  voltage  being
        read by one channel of a SAM module.

        50.2  CONSTRUCTION

        The SMDC is a rack-mounting unit that houses a standard Eurocrate card
        frame  into  which  is plugged a Logic Decoder Card (LDC) and up to 12
        Stepping Motor Driver (SMD) cards each of which drives 4 motors,  thus
        providing  control  for  up  to  48  motors.  It also houses two power
        supply  units.   All  connections  are  made  to   a   printed-circuit
        "mother-board" at the back of the chassis.

        50.3  LOGIC DECODER CARD.

        This is a single-height Eurocard which receives control  signals  from
        the  MMC  in  the  form  of  a six-bit address, a direction bit and an
        enable/strobe bit.  It decodes the first four  bits  of  the  address,
        which  determines  which  SMD  is  involved,  and  passes the last two
        address bits, together with direction and enable bits, to it.

        50.4  STEPPING MOTOR DRIVER CARD.

        This is a single-height Eurocard which takes the data  from  the  LDC,
        decodes  the  address  to determine which of its four motors to choose
        and moves it by one step in the direction  required.   Each  motor  is
        moved by application of the four phase pulses.  Individual motor logic
        keeps track of which phase was last pulsed.



        STEPPING MOTOR DRIVER CRATE (SMDC)                           Page 50-2


        50.5  MOTHER-BOARD.

        The motor driver currents are delivered over a 9-wire cable,  using  5
        wires  for  the  motor  connections  and  4  for  the  magnet position
        potentiometer.  Each motor has its own cable, hence  the  need  for  a
        relatively  dense  array  of  connectors (48) on the back of the SMDC.
        This array is combined with the backplane for the Eurocard cage.   The
        motor  connectors,  therefore, are be connected directly to the driver
        cards via traces on the backplane PC board.  Also provided on the  PCB
        are the connnectors to the SAM modules and to the MMC.

        50.5.1  Backplane Connector Pinouts:

              o  Three 36-pin AMP Connectosr to SAM modules.  J50, J51 & J52
                         Potentiometer slider voltage for Motors 1-32
                         J50     Motor 1         A1              A2
                                       |         |               |
                                       16        C7              C8
                         J51     Motor 17        A1              A2
                                       |         |               |
                                       32        C7              C8
                                 Ditto for Motors 33-47
                         J52     Motor 33        A1              A2
                                       |         |               |
                                       47        C5              C6
                                 Reference       C7              C8
                                   voltage
                 Note - In allocating one SAM channel for reading the reference voltage
                 applied to the potentiometers, it has been assumed that not more than
                 47 motors will be attached to one crate, although the possibility of
                 driving 48 exists.
              o  36-pin AMP connector  to  MMC.   J53.   For  pinout  see  MMC
                 chapter.



        STEPPING MOTOR DRIVER CRATE (SMDC)                           Page 50-3

              o  48 9-pin AMP connectors to motors.  J1 - J48
                                 Motor Phase 1  -  7
                                             2     9
                                             3     6
                                             4     3
                                 Motor Common      8
                                 Potentiometer
                                 12V Reference     5
                                           Gnd     4
                                         Wiper     1
                                           Gnd     2

        50.6  POWER SUPPLIES.

        There are two power supply units mounted in the crate:
              o  24 V 15 A unit for the motor current
              o  5 V 10  A  and  12  V  4  A  twin  unit  for  the  logic  and
                 potentiometers.

        50.7  DRAWING PACKAGE NUMBER

        233-105-01

        50.8  RESPONSIBLE ENGINEER

        M.  Browne / K.  Slattery