Conference hydra::amiga_v1

319.0. "Amiga Monochrome Hookup" by LEDS::ACCIARDI () Wed Feb 11 1987 18:53

    This article came into my hands recently... Some people have asked about
connecting an Amiga to a long-persistance monochrome monitor; this may help.
I have not tried this, and I don't personally know anyone who has, so proceed
at your own risk.  Monochrome monitors are cheap enough, anyway. ($79.00)

             Amiga Monochrome Adaptor for IBM Monochrome Monitor

                             by Dave Haynie



   This article details a circuit usable for interfacing the Amiga
computer to an IBM digital monochrome monitor.  This monitor requires an
inverted Horizontal Sync, and two bits of digital pixel data.  The first
gives the on-off pixel condition, the second the intensity.  The circuit
below mixes the Amiga RGB output to feed the IBM pixel input, and runs the
intensity bit straight through.  The Horizontal sync will be inverted; the
Vertical sync is buffered.

   The main reason you might want to use the IBM monitor is its high
persistance phosphor.  IBM normally drives this monitor with interlaced
video, so they use a phosphor capable of displaying interlace relatively
flicker free.  This circuit was built and tested at CBM with a CBM monitor
very similar to the IBM monitor, at least in Europe.  It was necessary to
modify the CBM monitor to display at a 60Hz rate instead of 50Hz; I don't
know if this will be necessary with the standard US IBM style monitor.  The
scan rate may also require a modification, this may depend on the
particular monitor you have.  Most monitors get their horizontal and
vertical timings from simple RC tank circuits, and the corresponding
controls adjust these values within a range.  Some have a very good range,
others are tight.  Usually an additional capacitor or resistor is all
that's needed for the monitor adjustment, though you'll probably need a
schematic if its required for your monitor.  Don't attempt this unless you
feel confident in your hardware-hacking ability.  


   Anyway, with all that said and done, here's the circuit:

   __                                                                   _
A |  |                                                                 | | I
M | 6|_________________________________________________________________|6| B
I |  |                                                                 | | M
G | 7|____|\|____________    1N914 x 3                                 | |
A |  |    |/|            |                                             | | V
  | 8|__________|\|______|_____________________________________________|7| I
R |  |          |/|      |                                             | | D
G | 9|____|\|____________|                                      _______|1| E
B |  |    |/|            |                                     |       | | O
  |  |                   \                                     |_______|2|
C |  |   +5v             / 470 Ohm                             |       | | C
O |  |    |              \                                    _|__     | | O
N |23|____|             _|__                         +5v      ///      | | N
N |  |                  ///                      c____|                | | N
E |  |       10K                               | /                     | | E
C |12|_____/\/\/\______________________________|/ 2N3904               | | C
T |  |                                        b|\                      | | T
O |  |                                         | \___                  | | O
R |20|______                                    e    |_________________|9| R
  |  |      |                                        |                 | |
D |19|______|                                        \                 | | D
2 |  |      |                                        / 470 Ohm         | | 9
3 |18|______|                           +5v          \                 | |
  |  |      |                            |           |                 | |
  |  |     _|__                          \          _|__               | |
  |  |     ///                   470 Ohm /          ///                | |
  |  |                                   \                             | |
  |  |                               c___|_____________________________|8|
  |  |       10K                   | /                                 |_|
  |11|_____/\/\/\__________________|/ 2N3904
  |__|                            b|\
                                   | \___
                                     e   |
                                        _|__
                                        ///

    interesting... I use an XT with a IBM Monochrome Monitor/Adapter
    in the next office regularly - never suspected that it was an
    interlaced screen.  Rock solid display, no jitters at all.  The
    long-persistance is annoying at first, but you get used to it.
    
    -dave

    I think the EGA 640 x 350 is non-interlaced.  The CGA 640 x 200
    is interlaced.  Personally, I stared at a ghastly green on black
    Data General D200 terminal for 8 years, and if I never see that
    combo again, it will be too soon.
    
    What I'd love to see is some smart person figure out a hack to send
    the Amiga 640 x 400 interlace into a nice Atari-type monochrome
    monitor, or maybe even a DEC VR201.
    
    I know the Atari monochrome scans at 71 hz, but maybe there is some
    way to get around this?