Proposal to use one mux bit  when under PC control


Ed's proposal for a "slight" redefinition of the interface to
    reduce the number of interface wires to match the limited interface 
    Ed purchased last summer -

I/O is logic level - 12 available 
DAC is voltage out of National Instrument interface box - 2 available
           should be diode clamped in Dick's box
ADC is voltage into National Instrument interface box - 8 available
           can be used to read logic from Dick's box
           and null voltage from Dick's box

--------------- Outputs from PC interface unit -----------------


I/O-00   \
I/O-01    |
I/O-02    |   0-9    Unit's digit
I/O-03   /

I/O-04   \
I/O-05    |   0-9    Ten's digit
I/O-06    |
I/O-07   /

I/O-08        0-1    Hundred's bit
                   *** please note, I cheat, ignore high bits of hundreds ***


I/O-09   one bit of Mux control        0 = Disk to seek     
        (other bits preset if PC)      1 = Track to seek
                                 

I/O-10    Output lines from PC above are valid, (wait 10 ms before accepting values?)
          However, the PC asserting this line will cause an immediate
               reset of the  "Operation Complete" status, goes to BUSY
          Asserting this line will cause motion, either disk seek or track seek.
          

Addressing conventions??   I'm flexible, what are good choices?

Disk    0-49??, ?1-50?, anything else is illegal, triggers Alarm/lockout
Track   "home" track is ???? (go here to seek another disk)
        "normal" tracks, 0 through 99 - as per Joe 
        Customer Engineering tracks identified as  -01,  ?100?, 101, maybe 102  - as per Joe
        maybe the PC is not responsible for accessing track -01?

DAC-0    - possible "logic level" output from PC
DAC-1    - possible "logic level" output from PC

-------------- Inputs to PC interface unit --------------------

I/O-11     Operation Complete,   (check error status) true==5 volts, "BUSY" == 0 volts
           "Ready for next command"
           operation can be
               - accepted  disk seek value, motion complete 
               - accepted  track seek value, motion complete
               - error status from Dick's box is valid

ADC-00      Error  (logic level) read as a logic level

            I propose that any error lock PC interface to "BUSY", zero volts
                 until manually reset at Dick's interface box.

ADC-01      Null point voltage  - (estimate goodness of detent position vs servo null
ADC-02     

ADC-03      
ADC-04
ADC-05 ... ADC-07

-----------------------------------------------
Joe responded July 26 with
"
Dick will need at least two bits for the 100's digit, since it has to 
represent four states:

> "normal" for tracks 00-99
> " >100"  for track 101 (and maybe 102)
> " <0 "   for track -01
> "home"   for the home position

I do not know the details of how he designed it, but it might be 
easier to use three bits (one dedicated unconditionally to the "home" 
or "not home" position)."
-------------------------------------------


To prevent damage and errors -
 1)   Dick's box is responsible for assuring that the arm is in home position
            before allowing disk seek.
     PC software will make a "best effort" to send "HOME" track position
         before sending a "Disk Seek" operation  -
         but strange things happen !!! - if nothing else, a bad contact
 2) Dick's box is responsible for hardware interlocks to assure reasonable safety.
      The PC interface is not wide enough, nor reliable enough to
          place this responsibility on the PC
 3) I propose that any error lock the Dick's box from further commends from
          the PC until manual reset of Dick's box.