From um-math!mailrus!ames!pasteur!ucbvax!decwrl!!weaver Sun Sep 18 04:57:30 EDT 1988

                NEC MultiSync II to Atari ST
                --- --------- -- -- ----- --
             Copyright (c) 1988 David S. Weaver
                   All rights reserved
This file may be copied freely only with the inclusion of the above
copyright notice for non-commercial use.
The NEC MultiSync II is an easy monitor to connect to your ST if
you want a monitor that can be used with systems other than just the
Atari ST.  The following text describes how to build a switch box
to connect the MultiSync II to the ST to allow use of color or monochrome
with the flick of a switch.
Some specs for the MultiSync II and Atari:
                        NEC MultiSync II                Atari
                                                low     medium  high
                                                ------- ------- -------
Horizontal Frequency:   15.5kHz - 35kHz         15.8kHz 31.5kHz 35.7kHz
Vertical Frequency:     50Hz - 80Hz               60Hz    60Hz    71.2kHz
Horizontal Resolution:  800 dots                  320     640     640
Vertical Resolution:    560 lines                 200     200     400
Signal level:           TTL pos                   ---     ---     ---
(analog)                0.7Vpp 75 ohm pos            1.0Vpp 75 ohm
Sync Signal level:      TTL pos/neg                  TTL 3.3K neg
(analog)                0.3Vpp neg                ---     ---     ---
As one can see from the chart, all the Atari specs fall with the NEC's
except for the 35.7kHz (instead of 35kHz) which doesn't seem to be a
problem.  Also the video signals are a bit high (1.0Vpp rather than
0.7Vpp), but it seems to be working just fine without the addition of
any resisters.  (If you want to add a resister, you would need 107-75
ohms or 32 ohms in series for the RGB signals, if I did my math correctly)
I initially had a problem with the NEC not syncing to high rez mode on
the ST after powering off the monitor and then powering it back on
again.  The workaround was to either unplug the video cable, or reboot
the ST.  I decided to add a switch to break the horizontal and
vertical sync lines.  During the process, I switched the cables I was
using to feed the DB9 connector to some that were more flexible because I
had a problem with the signal lines breaking at the connector.  I also
grounded the DB9 connector to the shield ground in the cable from the
Mega ST.  As a result of this rework, I found I no longer needed the
extra switch to interrupt the sync signals.

The following pin assignments are what work when connecting an NEC
MultiSync II to a Mega ST2 for color operation, they should work for
any of the ST series:
        MultiSync II                        Mega ST
        (female DB-9)                       (male 13 pin DIN)
        pin  1  red                         pin  7  red
        pin  2  green                       pin  6  green
        pin  3  blue                        pin 10  blue
        pin  5  mode control or v sync      pin 12  verticle sync
        pin  4  h/v sync or h sync          pin  2  composite sync
        pin  6  red ground                  pin 13  ground
        pin  7  green ground                pin 13  ground
        pin  8  blue ground                 pin 13  ground
        pin  9  ground                      pin 13  ground
    The Mega ST can also use this combination for sync:
        pin  4  h/v sync or h sync          pin  9  horizontal sync
        pin  5  mode control or v sync      *       not connected
    For monochrome to work, use the following connections instead of
    those listed for the same pins above:
        pin  1  red                         pin 11  monochrome
        pin  2  green                       pin 11  monochrome
        pin  3  blue                        pin 11  monochrome
        * Connect to pin 13 (ground) if you want to increase the
          vertical size on the screen.  Not really needed as the
          front panel "v size" switch has enough control, and the
          image size is big enough with the "v size" switch in the
          dentented position.
In addition, you will want to provide a separate RCA jack to provide
an audio out connection, given that the Multisync has no audio
            RCA jack                    ST connection
            --------                    -------------
            audio                       pin  1  audio out
            ground                      pin 13  ground

I ended up buying a "multisync" cable from Practical Solutions.
The Practical Solutions cable has the following color coding:
        Pin     Color               Function
        ----    --------------      -----------------------
          1     yellow coax         audio out
          2     black coax          composite out (composite sync on Mega)
          3     n/c
          4     red                 monochome monitor (ground for monochrome)
          5     n/c
          6     green coax          rgb - green
          7     red coax            rgb - red
          8     blue coax shield    +12V (may vary from ST to ST)
          9     black               horizontal sync
         10     blue coax           rgb-blue
         11     white coax          monochrome
         12     white               vertical sync
    The following was verified with an ohm meter:
         13     yellow coax shield  ground
                black coax shield   ground
                green coax shield   ground
                red coax shield     ground
                white coax shield   ground
    In addition the shield appeared to be grounded as well.
I cut about a 6" length of cable off the cable from Practical Solutions
and used it to wire in a few switches to switch both the monochrome/color
signals and the h/v/composite signals.  This cable is much more flexible
than the cable I tried using in my first attempt.  By separating the
individual shielded cables from the bulk wrap, you can get some very
flexible/thin shielded coax.

The switch box ended up something like the following:
             Atari ST pin       4 pole       NEC Multisync-II pin
           (13 pin DIN male)  double throw       (DB-9 female)
           -----------------  toggle switch  --------------------
                               |         |
    Blue Cx  10 - rgb/blue -------       |
                               |   /--------------- rgb/blue -  3
    White Cx 11 - monochrome -----/      |
                               |         |
    Green Cx  6 - rgb/green ------       |
                               |   /---------------rgb/green -  2
    White Cx 11 - monochrome -----/      |
                               |         |
    Red Cx    7 - rgb/red --------       |
                               |   /---------------- rgb/red -  1
    White Cx 11 - monochrome -----/      |
                               |         |
                - n/c ------------       |
                               |   /---------------- ground  -  9
    Red       4 - mono monitor----/      |
                               |         |
                                2 pole *
                              double throw
                              toggle switch
                               |         |
    Black Cx  2 - comp sync ------       |
                               |   /-------- comp/horiz sync -  4
    Black     9 - horiz sync -----/      |
                               |         |
                               |         |
    White Sh 13 - ground ---------       |
                               |   /--------- mode/vert sync -  5
    White    12 - vert sync ------/      |
                               |         |
    * This switch is purely optional, it allows use of both types
      of video sync, and will ground the mode pin to increase the
      vertical size when composite sync is switched in.
    Red Sh   13 - ground ------------------------ red ground -  6
    Green Sh 13 - ground ---------------------- green ground -  7
             13 - ground ----------------------- blue ground -  8
             13 - ground ---------------------------- ground -  9
    Yellow C  1 - audio out --------------------- RCA signal line
    Yellow S 13 - ground ------------------------ RCA ground line
             shield -------------------------------------- shield
    Note:  Do NOT connect pin 8 (Blue coaxial shield) to any other
           pins/signals.  This pin may have +12 volts on it.  Make
           sure that you insulate the shield very well on this line
           so it won't make accidental contact with another signal.

When the cable is all built, use an ohm meter and make sure that you
have no shorts.  When you actually want to hook it up to test it, set
the switches on the back of the MultiSync II to the following:
        Switch              State
        manual switch       on
        mode switch         gray    (shouldn't matter, digital only)
        color mode switch   64      (shouldn't matter, digital only)
Set the switches on the front to the following:
        Switch              State
        v posi              adjust after powering on
        v size              adjust after powering on
        h posi              adjust after powering on
        h size              on
        text                off     (shouldn't matter, digital only)
        text color          white   (shouldn't matter, digital only)
Now turn on power and you are on your way.  Note that for all of the
cabling of video signals, I used shielded cables (highly recommended)
and soldered all the coax shields together and to the ground pins
(use a smaller braided cable to actually connect between the shields
and ground pins).

   # Part#           Description                         Price:    Source:
   - -----           -----------                         ------    -------
   1 76108  16-130   1 7/16"x4 13/32"x3 7/32" black box    8.99    A/E
   1 69377  904      female RCA connector                  0.59    A/E
   1 276-1538        female DB9 connector, solder type     2.49    R/S
   1 53055  205817-1 female screwlocks (for DB9)           1.49    A/E
   1 22104  7401SYZQ 4 pole, double throw, toggle switch  10.99    A/E
   1 22048  7301SYZQ 3 pole, double throw, toggle switch   8.09    A/E
   1 76292  11-304   5/8" OD, 1/2" ID rubber grommet       0.99    A/E
   1                 Atari ST "multisync" cable           24.98    P/S
                                                 Total: $ 58.61
   Optional hardware for audio:
   1 277-1008B       200mW Amplifier-Speaker              11.95    R/S
   1 273-1552        9-Volt Battery Eliminator             4.95    R/S
   1 42-2444         6' Phono to Mini Phono Plug Cable     1.99    R/S
                                                 Total: $ 18.89
                                           Grand Total: $ 77.50
        P/S                        A/E                     R/S
   Practical Solutions        Active Electronics       Radio Shack
   1930 E. Grant Road         133 Flanders Road
   Tuscon, Arizona, 85719     Westborough, MA  01581
   (602)884-9612              1-800-343-0874
                              (617) 366-8899
You will also need various drill bits, solder, and some tool to cut a
hole for the DB9 connector into the plastic end of the aluminum/plastic
box.  The grommet is to protect the ST monitor cable entering the box.
    o This hookup worked for my Mega ST, I make no gaurantees it will work
    correctly on your ST, it has also been tested on a 1040 ST using the
    h & v sync and seemed to work just fine.
    o I have no connection with NEC, Practical Solutions, Active Electronics
    or Radio Shack.