raddison@nunki.usc.edu (Richard Addison) (03/19/89)
[A while back, I described my satisfaction with a particular monitor.]
I received several requests for an interface cable between the Amiga and
the Mitsubishi DiamondScan (AUM-1371A). So here is mine.
(In case you are wondering, the DiamondScan is one of the "multi-sync" type
monitors. I paid about $500 when I bought mine 18 months ago, so it isn't
the least or most exensive. In fact, I bought it before I bought my Amiga
2000. And just so you don't think I'm one of those people who didn't
recognize the Amiga years ago, I used an Amiga 1000 extensively in 1986.
I didn't buy the 1000 because by the time I had the resources to do that,
the rumors about a new Amiga were circulating. I waited a long time for
the 2000, and I am happy with it. But I digress.)
The main problem in making the cable is that you cannot connect HSYNC and
VSYNC directly from the Amiga to the DiamondScan because the DiamondScan
loads these signals so much that the Amiga thinks there is a genlock
connected. This prevents the Amiga from rebooting.
One solution is to buffer HSYNC and VSYNC between the Amiga and the
DiamondScan. I used a CMOS 4049 Hex Inverter to fix this curse (-;
because I had one on hand, but almost any inverting or non-inverting
buffer will work. (The DiamondScan automatically senses whether the
sync signals are positive or negative going.)
I placed the 4049 directly inside the hood of the connector for the Amiga
Video (female D-Sub 23 pin). This allowed me to get by with a 6 conductor
cable between the buffer circuit and the connector for the DiamondScan
Analog Video Input (male D-Sub 25 pin).
The circuit I used is presented below. Note that I grounded the unused
inputs to the Hex Inverter to reduce noise on the inverted sync signals.
For improved noise immunity, it would probably be wise to use twisted
pairs for each of the signals (Red, Green, Blue, HSync, and VSync) that
go to the monitor, but I get clean results with only a single ground.
Amiga DiamondScan
Video Video
Connector Connector
(D-Sub 23 pin) Interface Cable (D-Sub 25 pin)
RED 3 --------------------------- - - --------- 2 Red Video
GREEN 4 --------------------------- - - --------- 4 Green Video
BLUE 5 --------------------------- - - -------- 14 Blue Video
14|\ 15
~HSYNC 11 -----------------| >o----- - - -------- 16 Horizontal Sync
11|\ 12 |/
~VSYNC 12 -------| >o--------------- - - -------- 17 Vertical Sync
|/
GND 18 -------------------------- - - --------- 1 Sync GND
GND 20 ----+-- Vss (pin 8)
| 9|\ 10
+--| >o--nc
| |/ 7|\ 6
+------------| >o--nc
| |/
| 5|\ 4
+--| >o--nc
| |/ 3|\ 2
+------------| >o--nc
|/
+5V 23 ------- Vcc (pin 1)
(That's right, pins 1, 2, 4, 6, 10, 13, and 16 of the 4049 Hex Inverted
are not connected.)
Now why would anyone want to go through all of this trouble to use the
DiamondScan when other monitors are available that don't need the extra
work in making a cable? Well, how about the fact that flicker is much
less noticeable on the DiamondScan than on many other monitors. (I can't
give any measured results on this, but I have friends with standard Amiga
RGB monitors and the flicker is quite obvious on theirs, but not on mine,
even with the standard white on blue. I remember reading somewhere that
the DiamondScan uses phosphors with above average persistence. I wish I
knew where I saw that.)
Furthermore, I use my monitor for both my Amiga and my I*M AT (but I use the
Amiga a lot more!), so I use a standard cable with D-Sub 9 pin connectors
between the AT and the DiamondScan. Furthermore, I occasionally hook up my
VCR to the NTSC (composite video) input of DiamondScan. So, I can select
between the Amiga, AT, or VCR with a flip of a switch on the back on the
DiamondScan. Eventually I will wire a switch with better accessibility to
the D-Sub 25 pin Analog Video Input connector signals that select the video
source.
Finally, the DiamondScan allows me to use 704 by 470 "overscan." I put that
in quotes because every last pixel of it is visible! How can any of you be
satisfied with 640 by 200 or even 640 by 400? All this, and I still am not
using the "Automatic Tracking of wide range horizontal and vertical scanning
frequencies" feature of the DiamondScan. (The DiamondScan should work well
with the Flicker Fixer, but I get by well without it. Question for CATS:
Will any upgrade to the custom chips allow users to choose between NTSC and
PAL scanning frequencies? I'd love to use 704 by 525 or whatever the limit
Intuition imposes for PAL overscan.)
One final bonus: Here is my DEVS:system-configuration in uuencoded form.
Why would you want it? It saves you the trouble of getting "morerows" or
its substitute to set up 704 by 470 overscan. Furthermore, it has my color
preferences (amber, brown, dark blue, green) instead of the standard (white,
blue, almost black, orange) that helps reduce flicker even on the typical
Amiga monitors. It also has my custom pointer, because I think the standard
one is ugly.
Thanks for reading this far,
Richard Addison
"On a clear disk you can seek forever."
begin 600 system-configuration
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MP# @#^ 8& ?X#&8#G@9Y 88#7P" <8 #
M /\ "ZL EY $)0 ^P $D J>/M ($ + !G96YE<FEC
M 0!0 " ( !"
M (!9V5N97)I8P (T
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endVaxHeadroom@cup.portal.com (Joe William Walko) (03/24/89)
Note that on an Amiga 1000, the Mitsubishi Diamondscan apparently works find without any special mucking of the cable; on mine I hooked the HSYNCH and VSYNCH straight up and it worked fine.