MIT AI memo 105

Transcription of https://dspace.mit.edu/bitstream/handle/1721.1/6130/AIM-105.pdf

                MASSACHUSETTS INSTITUTE OF TECHNOLOGY
                             PROJECT MAC

Artifical Intelligence Project              Internal Memo No. 105.
Hardware                                    August 26, 1966


                 Modifications to PDP-6 Teletype Logic

                              Tom Knight


      The existing teletype logic for the PDP-6 has been modified to
accomodate up to four additional teletypes.  These were added with a mini-
mum of change to the existing logic, and are easily removable by taking out
the cable in 4M2 and replacing the cable in 4M1 with the jumper module.
      The additional hardware was designed to cause a minimum of change to
existing programs.  After pressing the console I-O reset key, current pro-
grams should behave exactly as they did previously.  (Note:  A CONO APR,
200000 does not have this effect.)
      Access to the additional teletypes is provided by five more bits
in the CONO to device 120 (Console TTY).  Bit 18 enables the setting of the
selection register from the other  four bit (e.g. CONO TTY, 400000 clears
this register).  Bits 21-23 specify which teletype is to be selected.  Until
this register is again changed, all I-O to device 120 is directed to the
selected teletype.  Bit 20 determines the ability of the various teletypes
to cause interupts.  When a one, the setting of the one flags in any of
the teletypes will cause an interrupt.  When zero, only the selected tele-
type is allowed to interupt.

Typical usage:
      CONO TTY, 400000
-Select Console TTY, inhibit interrupts from other TTYS.
      CONO TTY, 510000
-Select TTY 1, enable interrupts from all teletypes.

      A CONO which attempts to change the state of flags while also attempt-
ing to change the teletype number will reference the newly selected teletype
with, hopefully, no timing errors.
      On teletypes other than TTY0  (the console TTY) only bits 28, and
32-35 will have an effect on CONO, and only bits 30-35 are available on
CONI.  Bits 20-23 and 33-35 are available on CONI at all times.