Monday, September 5, 2016

Pleasant Suprises : The Epson MGA Q205A

Sometime ago, I acquired an 8-bit ISA card called the Epson MGA Q205A.  I figured it was a CGA compatible card because it had one DE-9 female port and one RCA jack, which the standard CGA configuration.  The only unusual thing about the card was a two-position switch on the bracket plate.  The switch is labeled color/mono.  I couldn't find anything about the card in Total Hardware '99.  I noted that the card displays in color on startup instead of B&W on a color composite monitor, I figured the switch was there to turn it to B&W.  An IBM CGA displays in B&W on startup in an IBM PC or XT.

After testing the card out a bit, I was pleased that it gave composite colors reasonably close to an IBM CGA card.  I was also pleased that the card is less than 10", meaning it will fit inside a Tandy 1000 computer.  However, Trixter's CGA Compatibility Tester demonstrated that the CGA compatibility was weak when it came to the 6845 tests.  This is not particularly surprising when I determined that the card does not have a 6845 CRT Controller onboard.  Since I have three IBM CGA cards, the card rarely has surfaced in my thoughts.

At some point recently, I thought it would be amusing to try the 8088MPH demo with the card and see whether it would suffer from an Epic Fail.  I have yet to see 8088MPH run perfectly and successfully unless the system was using an IBM CGA card and running at the IBM PC or XT's speed.  I installed the card into my XT and heard beeping.  I checked the switch and it was set to Mono, so I set it to Color and booted again.  This time the system booted.  I did not count the beeps, but it very well could have been 1 Long, 2 Short, indicating a fault with the graphics adapter.

To my disappointment, there was no Epic Fail with the Q205A.  Sure, the colors were a bit off, the wavy Kefrens Bar was cut off at the top and the music stopped and just output a constant tone during the Rotating Shapes, but the card made it through to the end of the demo.  The MOD music played back correctly notwithstanding the previous constant tone.

Since this card did not use a real 6845, I wondered if it showed CGA snow.  The good news is that it doesn't.  However I did notice that the demo seemed to show graphics effects a little slower than a geniune IBM CGA would.  When I tried my IBM CGA afterward, my suspicions were correct.  I think that Epson's 6845 clone may be slowing down accesses to the video RAM during the 80-column mode to avoid CGA snow.  CGA snow results from the 6845 trying to read the video memory when the CPU is accessing it.  8088MPH uses a lot of 80-column mode color text for its effects.

After exploring the Q205's CGA capabilities some more, I wondered whether the Color/Mono was really a CGA/MDA switch.  A Google search led me to this document, which strongly suggested that was the function :  I adjusted the dipswitches on the XT's motherboard, set the switch to Mono, connected my 5151 MDA and hoped it would not get destroyed.  The card showed the MDA bootup and text and worked just fine in Hercules Graphics Mode as the Product Bulletin had implied.  The text glyphs are not exactly the same as an IBM or Hercules card.  The < and > symbols are smaller than the IBM standard, for example.  You must turn off the computer, flip the switch, connect the appropriate monitor if necessary and then turn the computer back on for the mode selection to work properly and safely.

I never thought that the "M" in MGA meant "Monochrome", as in Monochrome Graphics Adapter but it presumably does.  Epson couldn't use "Hercules" in the product's name because Hercules is trademarked.  Actually, it doesn't stand for "Monochrome" but "Multimode"  I also thought that the memory chips were 16Kx1 bit chips given the markings of MB81416, but these are 64Kx1 bit chips.  Standard CGA cards have eight 16Kx1 bit chips while standard Hercules cards have eight 64Kx1 bit chips.  Since this card has 64KB of video RAM, it should be fully compatible with Hercules software.

There is no parallel port on this card or a header to add one, but there is parallel port circuitry in this card and it will take up LPT1/3BCH, so if you want to use a parallel port with this card, set it to LPT2/378H.

Since I had unexpectedly discovered that I had a Hercules Graphics-compatible card that could fit inside my Tandy 1000s, I sought to determine whether it would work with my older 1000s.  The TL, SL and RL series all have Hercules Graphics built-in, so whether the card worked in those machines was unimportant.  Whether it would work in a SX or TX was a question I had never determined for myself.

Fortunately, this card works in SX and TX, but you need to set Dip Switch 1 to Off in both systems so that the systems will initialize the monochrome display on bootup.   Otherwise, you will not see any text until you type the DOS command MODE MONO.  IBM advised in a dual MDA/CGA setup to set the startup display to the MDA to avoid damaging the monochrome monitor.  If you only have one display, you will be typing that text in the dark.  The card won't disable the built in Tandy Graphics Mode because Tandy and Hercules do not really conflict with each other.  If set to the CGA mode, the Epson card will disable the built-in Tandy Graphics Adapter.

The card will work alongside the Tandy Graphics Adapter in monochrome mode, although given that Tandy does not have snow, this is of less importance than with a CGA card.   It works as well as the Hercules support in the late Tandy's otherwise.  Unlike a Tandy TL, SL or RL, you can use the Hercules card alongside the built-in Tandy Graphics Adapter for dual-monitor support.   You may see some interesting colors and patterns on the Tandy monitor when using Hercules graphics because the memory areas of each overlap.  I would avoid a software reset with a Hercules card unless Dip Switch 1 is set to Off or the BIOS may fail to fully initialize either adapter correctly.  A hardware reset does not have any such problem. I am pleased to discover that the Epson MGA Q205A is a much more interesting card than it first appears.

No comments: