View Full Version : MaxLogic MX657 EGA/VGA card - Adventures In Jumper Configuration

August 18th, 2010, 12:48 PM
So, not too long ago, I purchased a combination EGA/VGA card off eBay for use in my 286 (you can see a picture here, (http://cgi.ebay.com/Maxlogic-MX657C-16-Bit-ISA-EGA-VGA-Video-Card-/260364466173?pt=PCC_Video_TV_Cards) where there's another one offered for sale.) As near as I can tell, it's a VGA that outputs to CGA/EGA monitors, rather than vice versa, since it's loaded with a full 256KB of RAM, but since I still have to finish wiring up the DB9->PCjr connector, I haven't gotten around to testing it yet.

My plan, since I'd previously found an MDA/Hercules clone at the recycle center, was to use the mono card with a monochrome monitor I acquired with the computer for normal DOS operations, and hook the EGA up to my very nice PCjr monitor for game/graphics stuff. Problem was, plugging both cards in at once caused the BIOS to do all its text output to the color card, and I couldn't figure out which of the 8 DIP switches would correct this, since there seems to be absolutely no documentation for the thing ANYWHERE on the Internet. Even the TULARC PC reference (http://stason.org/TULARC/pc/) had nothing on the $%#& card.

However, having already shelled out perfectly good money for the thing, I figured I'd try and work out the jumper settings manually. This thread is where I'll document my attempts, for the record and for anybody else who happens to stumble across one of these.

Some basic information: there is an array of 8 DIP switches on the back of the card, between the VGA and RGBI connectors; they are numbered 1 through 8. There's also a single jumper on the board, but I have a feeling that that's probably not a configuration thing; it's in the open position, and I'm going to leave it there unless I have reason to suspect it does something.

My first experiment involved counting binary through the different combinations of switch positions, stopping when I finally got the computer to boot in MDA mode (my initial goal.) From this, I figured out two things.

First (though I discovered it last, to my chagrin,) switch #5 controls the boot mode. When it's off, the computer boots with the active display on the color card; when it's on, it boots on the mono card.

Second, switches 1-4 seem to be a single group, since the computer complains via POST beep if all of them are off, but works fine when any combination of them are on. My guess is that this group may control the initial video mode for the card, but I have yet to test this.

I still don't know what switches 6-8 are for.

Anonymous Coward
August 18th, 2010, 08:06 PM
Did you already try using the switch settings for this card?

August 19th, 2010, 03:02 PM
I did; despite the similar arrangement, it doesn't seem to be the same card.

December 14th, 2010, 08:56 PM
Well, coming back to this thread after only four months - I have an EGA monitor now, and have made a little progress in understanding the card. For starters, it's a "MaxLogic Max/16," as it identifies itself on bootup. I can't find anything on it by that name either, though. I'm beginning to understand the switch functions a bit better:

Switches 6-8 are lock switches that disable CGA, EGA, and VGA modes, respectively (presumably to prevent damage to sync-sensitive monitors by disabling higher-resolution modes? I dunno.) Switch 5 does control whether it boots with the MDA as the active card or the EGA, as it seemed.

Switches 1-4 are still a mystery, though - turning on switches 3 or 4 causes it to do a weird thing where the first character of each text line on the EGA monitor appears at the end of the previous line, like it moves the screen address to (base - 1.) This also causes the left 1/2 to 2/3 of graphics-mode displays to be cut off entirely - beats me what this is all about. Switches 1-2 don't appear to do anything, except that the POST will beep if one of them isn't on.

The big issue for me is that I can't seem to get the EGA/VGA and MDA/Hercules cards to coexist like I want them to. Turning on switch 5 boots DOS in MDA mode, but EGA and VGA video modes won't work (CGA seems to, though.) From what I read, this may be an issue with the MDA/Hercules card, so I might have to fiddle with that. If anybody knows of anywhere to find documentation on the MaxLogic card, I could really use it.

December 15th, 2010, 01:53 AM
I thought you set it in the BIOS/Setup of your 286 to use color or monochrome as primary adapter.

December 15th, 2010, 05:37 AM
Yeah, for some reason my computer ignores that. But that's not the problem, anyway - the issue is that setting the MDA as the primary display seems to be disabling the EGA/VGA modes for some reason...