CAMAC 177 Timer Module

                                  A. Franck

                               November 4, 1983


   General Description:

        The basic function of the CAMAC 177 MODULE  is  to  provide  timing
   pulses  at  a  programmable  delay  from selected tevatron clock events.
   Eight timing channels are provided.   Each  channel  may  be  programmed
   independently with respect to delay and clock events.

        The delay is established by using a  programmable  clock  frequency
   and a programmable down counter.  The clock may be set to frequencies of
   1 MHz, 100KHz, 10KHz, or 1KHz.  The sixteen bit binary down counter  may
   be loaded with values up to 65,535.  The clock is derived from the 10MHz
   Tevatron clock signal and synchronized to  the  trigger  event,  thereby
   producing jitter free timing pulses.

        The clock events to be used as  triggers  are  selectable  and  may
   include any of the possible 256 events.  A maximum of fifteen events are
   allowed per channel.  A RAM is used on the module as the storage  medium
   for events.

        The timer is resettable, meaning that any trigger  event  occurring
   during  the  timing  period will restart the timer.  Once timed out, the
   channel is quiescent until it is retriggered by an event.

        The eight channels may be enabled and inhibited either singly or as
   a  group.   The  state  of  any  channel  (inhibited  or enabled) may be
   obtained through a status read.

        A jumper provision is made to  allow  wire  ORing  of  the  channel
   outputs.   This jumper is located prior to the output drivers and allows
   a  variety  of  output  configurations.   Possibilities  include:   each
   channel driving it's respective output, all channels driving one output,
   one channel driving all outputs, etc.

        Provisions are made for an external clock and  an  external  reset.
   These  are  to be used together as an alternative to the Tevatron Clock.
   If the external clock frequency is less than 10MHz,  the  time  must  be
   scaled accordingly.  A DIP switch is provided to allow selected channels
   to respond to the external reset signal.

        Module LAM is generated only upon absence of clock  signal,  either
   Tevatron or external.  LAM status may be obtained through a status read.



   OPCODES:

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