COMPUTE II ISSUE 2 / JUNE/JULY 1980

The Single-Board 6502

Eric Rehnke

MTU Graphics

I received the Micro Technology Unlimited Visible Memory board a short time ago and have been working on application ideas for this rather unique board.

For those of you not familiar with it: Visible Memory is both an 8K dynamic RAM board with invisible refresh AND a 320x200 bit-mapped video graphics board.

This clever design makes use of the fact that the video circuitry must read the entire 8K block at specified intervals and allows it to serve the double purpose of also refreshing the dynamic RAM. You're wondering why you didn't think of it, right?

“Bit-mapped” means that every bit in the 320x200 screen matrix is represented by one bit in the screen memory. With this board, one has total control over every pixel. It's very similar to the Apple hi-resolution graphics in that respect, with the exception that the MTU board is slightly denser (320x200 vs. 280x193).

MTU also has some software available for this board that could, assuming you owned an AIM-65, turn your computer into a low cost version of the HP-85. One software package works together with AIM Basic to allow such things as mathematical functions to be graphed out on the display while another software package allows the built-in AIM printer to record whatever pattern is on the screen. How does that sound? That same software also allows text lines up to 80 characters in length to be printed SIDEWAYS on the AIM printer for increased readability.

My appreciation for AIM increased considerably when I saw it performing in this fashion.

Without any further software work, the AIM 65 coupled with some MTU hardware would seem ideally suited for duty in the laboratory, the classroom or most anywhere that a relatively low-cost graphics system can be justified. Assembling such a system turns out to be very easy. It can be performed by someone with moderate electronic skills and with totally “off-the-shelf” components.

But don't let your imagination stop here. Many other things can be done with such a display. How 'bout a 16-channel digital logic analyzer? Very possible with a bit-mapped graphics display.

Want to make your KIM, AIM, or SYM look like a PET? Simple.

PET's screen is organized as 25 lines of 40 characters each. Each of these characters is composed of an 8x8 dot matrix. Multiply 40 characters times 8 bits (character width) and what do you get? Why 320, of course. Then do the same with 25 lines times 8 bits and you get 200.

So, when you break down PET's display to the dot level, the MTU and PET display are precisely the same. It is possible to generate all PET's graphic characters in software or design your own special purpose characters for that matter.

Get the picture?

The Apple and Atari can be simulated in precisely the same fashion. Foreign language fonts are also possible.

Normal X Y plotting subroutines are also included in the MTU graphics software.

You can get more information on these and other products from

Micro Technology Unlimited
P.O. Box 4596
Manchester, NH 03108
(603) 627-1464