jalbert@cs.ubc.ca (Francois Jalbert) (07/24/90)
Hello everybody. I just finished reviewing a few adapters and bought one
of them. I thought I'd share with all of you my findings. I also have a
few problems and I'd like to hear what you've got to say about them.
OK, I've got a 12/8 MHz 80286 with 4Mb of RAM and 0/1 wait states on the
main 640Kb (Read/Write) of memory. I've got a Dexxa serial mouse (Logitech
made I believe), 1 parallel and 2 serials. I use PC-DOS 3.3 which has been
patched with debug to allow me to use DRIVPARM for my B: drive which is a
somewhat unusual 720Kb 5 1/4in drive.
My usual supplier gave me the following three choices with prices in Canadian
$$$:
OAK VGA 16-bit 256Kb $100
Trident VGA 16-bit 256Kb (handles 512Kb) $130
ATI VGA 16-bit 256Kb? (handles 512Kb) $200
I use the popular (and very handy) ATPERF (available at SIMTEL) to check the
access time of these cards on a 25 MHz 80386 machine at the dealer's place.
OAK VGA 1.4 usec on 8-bit operation, 2.8 usec on 16-bit operation.
Clearly an 8-bit card. I tried changing jumper positions and could
not get it to run in 16-bit mode. Any comments anyone?
Trident 1.4 usec on 8-bit and 16-bit operations. Be careful!!! The
documentation is wrong concerning the jumper settings. I had
to fiddle with it before it began to run in 16-bit mode. Or
I'm too stupid to read documentation correctly.
ATI VGA 1.4 usec on 8-bit and 16-bit operations. No problem here.
So, I was surprised to see such identical access times. We're looking at
about 30 artificial wait states added by the VGA adapter on that 80386.
Each adapter had various super VGA modes that don't interest me. I'd rather
keep it simple and I can't afford a fancy monitor anyway. But in general,
the more expensive, the fancier the card.
I tried a few CGA/Hercules/EGA/VGA applications and games. I found:
OAK VGA Hercules not fully compatible. I had trouble sometimes when
using Borland compiled stuff. CGA not fully compatible given
old "dirty" PC games.
Trident Hercules OK. Better at old CGA games. The mode switching
program allows you to turn the adapter into a more compatible
CGA mode before rebooting. Then, all CGA games worked OK.
I was impressed.
ATI VGA Hercules OK. Trouble with some old CGA games. I didn't look
if any rebooting/reconfigurating program was supplied. The
difference in price vs Trident was too great for me.
So I bought the Trident VGA (256Kb) with a SamTron SC-431VII which has
a 0.31mm dot pitch. Further extensive assembly language experimentation
left me very happy with the register-level compatibility in the various
modes. Trident did their homework. The card has a BIOS at C000H which
provides integrated operations in the various modes. Beware that this
could interference on some machine that need the area for buffers.
Now my problems. First a minor one. The Samtron screen generates distortion
on a nearby old text-only monochrome PC screen. I've determined the problem
remains if the video signal is disabled (screensave). My "theory" is that
the noise is on the power line. The undesirable motion of the monochrome
characters has an amplitude which is fairly minor (1/10th the height of the
monochrome characters) but it is distracting. Anybody has any experience with
that sort of phenomena. I have never heard of it, but I do lead a sheltered
life!
A somewhat more serious problem has to do with quick writes to the video
screen, or scrolling. Some characters don't write at all, the old characters
remain on the screen. So you get a mixture of the old and the new screen.
This is particularly obvious with PC-Write Lite where pressing Esc generates
a 3 line long help menu overwritten over the text. Pressing Esc again should
remove that 3 line long menu and restore the text. But the job gets half done
with some text restored, and some help text remaining. Other applications
suffered from the very same problem. Trident supplies you with a mode switching
program, and I know these beasts have a tendancy to stay partly resident and
perhaps correct known bugs of their respective adapters. So I tried it and
indeed 2Kb remained resident. That solved the problem! But then ATPERF told
me the card was now running in 8-bit mode! Thas is 1.4 usec 8-bit operation
and 2.8 usec 16-bit operation. That tells me the problem is not with the
RAM being too slow, it's with the decoding circuitry. The card has a slow
address decoding jumper which I may try one day. But I am disappointed that
the card apparently can't handle an 8 MHz bus speed. My dealer told me his
experience with prior models of the Trident adapter was bad with several
of them freezing while scrolling. Mine isn't that bad, but I'd like to get
16-bit operation out of it. Anybody has any comments/experience to share?
Finally, some games don't "see" anymore my Dexxa mouse. I've tried different
mouse drivers, using the Trident mode switching program, its various
compatibility modes, to no avail. I am starting to doubt that my mouse driver
is to blame by being too old. Anybody has any info on such problems? When
loaded, my mouse driver does say "EGA connected, driver installed." I deduce
that the presence of an EGA/VGA adapter influences the way the mouse
operates since there was a need to detect its presence while installing
the mouse driver. Perhaps they share some hardware interrupt. I don't
know enough about mice. I just know their software interrupt and sub-functions.
That's all folks! I await anxiously your comments. Overall, I'm very happy
with the register-level compatibility of the Trident VGA. It's various
80/132 column and 25/30/43/60 line modes also work hand in hand with PC-Write
Lite. And it's various compatibility modes are always detected correctly
by the various programs I tried. I was particularly concerned about Borland
compilers since I'd heard stories. But all appears fine.
Regards, Franky