MiniTerm Merlin video board chipset...kind of

[mountainking]

(I know this probably belongs in the showing off your collection section but whatever....)

This was one of those buying without thinking it through first kind of purchases and one which I regretted right after I pulled the trigger so I figured I'd make a post to try to get something more out of the purchase. The manual is something I already had but I figured I'd pad the post with it because it's pretty awesome.

So I saw this MiniTerm Merlin video board chip set for $30 and I pulled the trigger without really thinking about what I was actually buying and then immediately afterwards I thought "why the hell did I buy this, there a bunch of things that I would have rather spent that $30 on ". Oh well, it is kind of cool even without all of the chips, just not $30 cool. Guess it can be a source of early-date-code logic ics. The manual on the other hand, which only cost me $10, is fantastic as it has tons of hand written notes on the pages of the manual as well as a bunch of added pages with handwritten notes. It also, for some reason, has a Cromemco 3K Control Basic Instruction Manual in the middle of the binder . I love handwritten notes in docs, they make something like a manual feel more like a journal .

P.S.- I love how prevalent cartoon characters were in the 70s

 

[Al Kossow]

The manual on the other hand, which only cost me $10, is fantastic

are you going to scan it?
I looked at the listing and thought 'meh.. he pulled all the high-value mos parts'

 

[mountainking]

are you going to scan it?
I looked at the listing and thought 'meh.. he pulled all the high-value mos parts'

I believe the manual is available online already, no?

That's what I should have said, lol, but I was tired and not thinking clearly. Most of the ics that are missing are fairly easy to find, hell I may have all of them in my workshop already, but having ics from the same time period would give the set more value, though I suspect that this is just the result of someone trying to gather up all of the ics for a project and the person just never accumulated all of the ics, who knows. Apparently this is all that remains from a large collection that the seller bought years ago, all except for an Altair which the seller is not ready to let go of yet.

 

[Hugo Holden]

I am interested in S-100 video cards, for example I have the one from PT for text and two from Matrox, the ALT 256 and ALT512 for graphics, the Dazzler and another for color graphics.

I have never seen or heard of this card.

Can you explain what it is/does ? It seems interesting.

Does it have its own video memory or does it hijack the computer memory with DMA ?

How many programmable pixels is the video display, what format ? Can it do a grey scale or just on-off pixels ? Was it intended for a monochrome or color display ?

 

[mountainking]

I am interested in S-100 video cards, for example I have the one from PT for text and two from Matrox, the ALT 256 and ALT512 for graphics, the Dazzler and another for color graphics.

I have never seen or heard of this card.

Can you explain what it is/does ? It seems interesting.

Does it have its own video memory or does it hijack the computer memory with DMA ?

How many programmable pixels is the video display, what format ? Can it do a grey scale or just on-off pixels ? Was it intended for a monochrome or color display ?

I don't know too much about the board but you can find some info here:

S100 Computers - MidTerm Associates- Merlin Board

S100 Computers

www.s100computers.com

Note they call the company "Midterm" instead of MiniTerm.

Here is some more info on the MiniTerm Merlin:

deramp.com

deramp.com

Hope some of that helps answer your questions.

 

[Eudimorphodon]

Can you explain what it is/does ? It seems interesting.

Does it have its own video memory or does it hijack the computer memory with DMA ?

Ugh. The manual fragments that are available online do an absolutely terrible job actually describing the working theory of the card. (There's a hardware assembly manual and a manual for the ROM software, but neither has any really useful description of the hardware working theory.) But from what I can glean it looks like it uses DMA with a theoretical maximum resolution of 320x200. (It has a 7.9Mhz pixel clock.) There's a small amount of RAM on the board that I think *may* act as a programmable character memory but, again, the documentation is pretty terrible.

A kind of interesting feature I gleaned from it (if I'm interpreting this correctly) is it looks like it supports a "sparse" memory architecture kind of like that in the Sinclair ZX-80, IE, it can recognize end of line/end of screen markers. So for instance, if you're displaying a "40x25" text screen you don't necessarily need to consume 1K of system memory via DMA; if you're only displaying one character on each line you'd only consume 50 bytes of memory

 

[Chuck(G)]

The Intel 8275 CRTC can be programmed to work that way. You can either use the "visible" attribute mode or the "invisible" one which allows for lines of varying length in memory as well as hiding the positions taken up by attributes. I once started to program in that mode, but found the bookkeeping to be a nightmare.

 

[mountainking]

Ugh. The manual fragments that are available online do an absolutely terrible job actually describing the working theory of the card. (There's a hardware assembly manual and a manual for the ROM software, but neither has any really useful description of the hardware working theory.) But from what I can glean it looks like it uses DMA with a theoretical maximum resolution of 320x200. (It has a 7.9Mhz pixel clock.) There's a small amount of RAM on the board that I think *may* act as a programmable character memory but, again, the documentation is pretty terrible.

A kind of interesting feature I gleaned from it (if I'm interpreting this correctly) is it looks like it supports a "sparse" memory architecture kind of like that in the Sinclair ZX-80, IE, it can recognize end of line/end of screen markers. So for instance, if you're displaying a "40x25" text screen you don't necessarily need to consume 1K of system memory via DMA; if you're only displaying one character on each line you'd only consume 50 bytes of memory

Wow, man, you are REALLY into video tech! Not that that's a bad thing. Most of that went completely over my head, though I do have an interest in the video generating circuits of these early microcomputers, I just haven't dug too deep into them, yet.

Back in the early days of the microcomputer there were a bunch of new companies popping up, often putting out stuff with technology that they "borrowed" from other people's designs so sometimes they didn't even completely understand the technology they were putting out. Another reason why they may not include a detailed description of the video section is that it wasn't necessary, most of the people who were reading the manual probably wouldn't even understand the minute details. You have to realize that this was a time before the information highway so even someone like you with such a strong interest in a particular technology might not know or understand the technology completely because the information simply didn't exist and if it did it was in some book that you had no way of accessing or maybe the information was only in a select few people's heads.

As far as the information that you found online about this board's circuit function, was it just too vague or do you think the bits and pieces you found are a part of a larger, more in depth body of information, as in you are missing some pages? Did you find a schematic for the board? Seems like that would tell you most of what you would need to know about the circuits, though that's assuming you understand circuit design.

 

[Al Kossow]

perhaps you should just scan your copy to see if there is anything in there that is missing from
what appears to be incomplete on line.

 

[Eudimorphodon]

Did you find a schematic for the board? Seems like that would tell you most of what you would need to know about the circuits, though that's assuming you understand circuit design.

Like I said, all that's in the two manuals I could find online are a hardware assembly guide (which is 95% "stick these parts in these holes and put the card in the machine and apply power to see if smoke comes out before moving to the next step“) and a software guide for an optional add-on ROM which is a mix of functional descriptions of the software on the card and some documentation about how to patch programs like MS BASIC to use the card for I/O instead of a terminal (again, using their driver software). The only "hardware level" programming information is a very terse section at the end of the assembly manual which says how to key in some short programs on your front panel (yes, really) to brute-force stuff some values into the control register (which seems to use a really oddball serial method of loading values) to see if the hardware has the magic smoke inside.

And no, the schematic is not in either of the two manuals I found, so even if I wanted to sit down and laboriously reverse-engineer the working principles of the card just from the parts I don't have that option. I mean, I guess the assembly manual has the PCB traces and a parts layout guide in it so I suppose you could recreate it, but life is way too short for that.

Back in the early days of the microcomputer there were a bunch of new companies popping up, often putting out stuff with technology that they "borrowed" from other people's designs so sometimes they didn't even completely understand the technology they were putting out.

Again, maybe there's a manual that actually has the goods in it. In fact, I think there'd have to be because it would be a massive PITA to try to write software from scratch for this board with what's out there. The manuals for every other S100 video card I've looked at vary in quality widely, but all of them had enough "API information" in them for someone who can't tell which end of a soldering iron is up (but does know how to program) to know which I/O port or memory range does what. You could make some educated guesses about *some things* from the brute-force register stuffing test programs, but that's about it.

 

[Eudimorphodon]

perhaps you should just scan your copy to see if there is anything in there that is missing from
what appears to be incomplete on line.

The OP’s photos show a “Users Manual” with a listed section specifically titled “Hardware Theory”. This is not on either Deramp or S100computers; again, all they have is the assembly guide and the docs to an enhanced Z80 ROM add-on.

 

[mountainking]

perhaps you should just scan your copy to see if there is anything in there that is missing from
what appears to be incomplete on line.

I guess I should, though it would a laborious task, it's a thick manual, about an inch and a half of double sided pages, though one of the reasons I collect is so I can help preserve and archive the pieces in my collection that are not archived already. And I think this copy, with all of the handwritten material, would make for an extra special version of this manual. Guess I need to figure out what the best way to scan the manual is

 

[Al Kossow]

thank you!

 

[Eudimorphodon]

FWIW, The November 1976 issue of Byte has a review of this board, along with a pretty ad for it on page 20.

The review doesn't have any information about how to actually program it, but does describe the hardware reasonably well. According the article (and the ad) the board does indeed rely on DMA; the tiny bit of RAM which is *optional* on the card is intended as scratchpad memory for use with the software option ROMs. In character mode is uses the ubiquitous Signetics 2513 character generator (ala the Apple II), in graphics mode the board could use up to 2K of DMA memory to do 160x100 monochrome graphics. Support for 320x200 graphics and color via a future add-on board was "coming soon".

 

[mountainking]

Tomorrow I will post of more of the manual, there are pages of programs along a ton of other information, like I said, it's a thick manual.

 

[mountainking]

So it wasn't until I posted the original pics I took for this post that I realized that this manual is a "preliminary and incomplete copy of the Merlin User Manual". I picked it up recently and had only flipped through it casually but I have now gone through it thoroughly and here is what's included and what is not:

Section I - completely missing

Section II - complete

Section III - appears to be complete (MBI listing)

Section IV - completely missing

Section V - appears complete

Section VI - complete

Appendix - ASCII CODE and IC PINOUTS only, all else missing

MEI ROM Software Documentation - complete

Interfacing Merlin To The TDL System Monitor Board - complete

MCAS (Merlin Cassette) Documentation- complete

ROM/EROM Documentation - complete

(I can only attach 10 pics so I will add the rest of the pics of the sections listed above in a post after this one)

So most of the manual is there, and really while it's a drag that the hardware section (Section I) is completely missing, the all important software listings is there and complete so it's not that bad. I plan on scanning the manual in the not too distant future, I'm bust w my business at the moment and will be moving soon so I will probably wait til I am settled into my new place to do the scan. In the mean time if anyone wants to see a particular page or pages lmk and I will

 

[mountainking]

Here are the pics of the other sections that I could fit in my previous post.