UET Discussion-4
                      ----------------
                                                         (RK)(11/13/97)
                                                              (misc126)

     The following document is arranged in the form of a series of
  questions that need to be addressed reg. the the new UET and Timer
  design. The answers are mostly speculative at this time. The purpose
  is to start discussion of these topics.

   (1) How can the UET be started and stopped ?

       Ideally, we would want there to be two modes, a program start/stop
      and an external start/stop mode. Furthermore, the external start/stop
      should allow for a software selectable input number.

   (2) Can the timers be started after the UET timing has been started ?

       In a simple sense the answer is yes, since we can introduce a 
      delay with the timers, but the real question is: Can the timing
      sequence be changed after the UET timing has begun ? For example,
      can the host PC ask the PC-32 to "turn the DSS (or some light) on
      for 500 msec" after the UET timing has already begun ? 

   (3) Can the UET be started after the DSS timers have been started ?

       This is something that probably doesn't need to be done often,
      if ever. I mention it only in case anyone else knows of some
      application where this may be important.

   (4) Can UET channels be selectively enabled/disabled ?

       In most cases we only want to sample one UET input channel (# 0).
      It is necessary then to disable all other input channels. It is not
      enough to ignore them in software, since there may be noise (60 cycle
      or radio freq.) on any other cable that is plugged into other
      input channels not in use. This may overload the host PC, or cause
      buffer overflows.

   (5) How can the UET timer be reset to zero without stopping the UET ?

       This is necessary at the start of each new repetition. This should
      be selectable between DSS-1 and DSS-2, at least.

   (6) How many timers are available ?

       The present information seems to suggest 32 independent timers.

   (7) How many output lines are available ?

       The present information seems to suggest 32 independent lines.
 
   (8) How will parameters other than timer be set ?

       Examples of these parameters are: DSS frequency, A/D sampling rate
       etc. Should some of these be set directly on the PC-44 ?

   (9) Can parameters be changed while timing is in progress ?

       For example, can tone frequency be changed during the "off" time
      between reps ? This feature is used in some existing programs.
      This implies that the host PC be able to sense whether the 
      "duration timer" is on or off.

  (10) Can we terminate the UET and Timers prematurely ?

       For example, by a "cancel" command to the PC-32.

  (11) How does the UET pass error conditions and other special events
       to the host PC ?

       For example, buffer overflow, bar pressed, etc.

  (12) How does the UET convey DONE event to the host PC ?

  (13) Is it possible for the host PC to "sense" the state of any timer ?

  (14) Is it possible to set a time base other than the fastest possible ?

       Potentially useful for long-term (e.g. overnight) monitoring of
      slow events.

  (15) May be desirable to add a self-test mode to the UET program, which
      could be run periodically to check for hardware errors or drift.