Article 41817 of comp.sys.dec:

In article <333953cd.0@news.oit.umass.edu>, asvirsky@emily.oit.umass.edu (Alexander R Svirsky) writes:
:What is the pinout for this round DEC mouse?

   The old-style "puck" pinout and signaling protocols are definitely
   not even remotely compatible.

   Either get a puck mouse, or get a PC mouse, depending on what you
   are up to...

   However, to in order to convince you that you don't want to try this:

   Serial communications at 4800 baud +/- 2%, start bit, eight data bits,
   odd parity, one stop bit.  Position reports are encoded into three 9-bit
   (8+parity) bytes.  Commands to the mouse include R: select incremental
   stream mode (powerup default is prompt), D: select prompt mode, P:
   position request (implicitly switches to D mode), T: run self-test and
   identify (returns four bytes, indicating firmware ID, hardware ID, error
   code or zero, and button code or zero).  The data bits in the position
   request report look like this:

   7  6  5  4  3  2  1  0	l,m,r: buttons; depressed if 1
   1  0  0  sx sy l  m  r	sx,sy: x & y sign bits; 1 = +
   0  x6 x5 x4 x3 x2 x1 x0      x6-x0: X displacement, x0 is lsb
   0  y6 y5 y4 y3 y2 y1 y0      y6-y0: Y displacement, y0 is lsb

   The connector pinout:
	1	signal and power ground
	2	TXD (from mouse)
	3	RXD (to mouse)				  +
	4	-12V					5 6 7
	5	+5V					3    4
	6	not used				+1  2+
	7	device present (shorted to pin 1)
	shell	protective ground			+=key

   There's a rather large write-up on the puck protocol in the
   _VCB02 Video System Technical Manual_, EK-104AA-TM.  (The above
   will likely not be enough information for one to to correctly
   operate the puck from j-random system -- assuming the necessary
   "converter widget" can be designed and implemented, of course.)

  -------------------------- pure personal opinion ---------------------------
   Hoff (Stephen) Hoffman   OpenVMS Engineering   h*ffman@xdelta.enet.dec.c*m
     headers and addresses munged to avoid automated spammers: junk-e-mail