AppleTi and F18A at KansasFest

Years ago, I outlined interfacing the F18A, a TMS9918A Video Display Processor (VDP) clone with VGA output, to the Apple II.  I never followed through, but somebody on the AtariAge forum recently completed a design and released a PCB.  The “AppleTi” board is a functional clone of the E-Z Color Graphics Interface.  The AppleTi board only supports the F18A, not the original TM9918A, and is the simplest interface possible with only a single 74LS00 NAND package generating read/write control signals.

The VDP interfaces to the 6502 via two memory-mapped byte-sized registers selected with the MODE pin.  The AppleTi interface connects MODE to the Apple’s A0 address signal.  Combined with the “DEVICE SELECT” decoding on the Apple II motherboard, this design shadows the VDP registers across the 16 byte slot-specific address space ($C0n0 – $C0nF where n is the slot number plus 8).

The practical consequence is that the AppleTi is mostly-kind-of-sort-of compatible with software written for the Synetix SuperSprite and Third Millennium Engineering Arcade Board.  I say “mostly-kind-of-sort-of” because code that accesses the VDP is compatible but code that expects sound or video switch hardware won’t work.  Most of the sample code from Synetix and Third Millennium won’t work.  For the software that does work, there is minor VDP screen corruption from sound and video switch initialization attempts.  However, despite these limitations, the AMPARCADE library from Third Millennium and the StarSprite library from Synetix do function well enough to be useful with the AppleTi/F18A board.

At KansasFest 2016, I shared an introduction to the VDP, AppleTi, and programming the board with the AMPARCADE library.

Over the next month, I hope to create a series of posts with a tutorial introduction to VDP programming.

ImageWriter II: Essential hardware for every system

NOS ImageWriter II ribbon: The rubber roller has turned to sticky goo.

NOS ImageWriter II ribbon: The rubber roller has turned to sticky goo.

Back when my Apple IIc+ was my only computer, I really wanted an ImageWriter II printer.  This was “the” printer to own.  It was reasonably fast, compatible with nearly all Apple II software, and printed in glorious color.  Unfortunately, I was a kid with no job, and an ImageWriter II cost over $500.  Needless to say, I never owned the printer back then.

More than 20 years later, I finally own an ImageWriter II.  Thanks to Sean’s Garage Giveaway at KansasFest a few years ago, I walked away with a nice condition printer, a stack of NOS color ribbons, and a used black ribbon.  The color ribbons, despite being never used and sealed in plastic, were dead due to age.  An orange rubber roller internal to the ribbon cartridge had turned to some sort of nasty goo.  Every “new” ribbon I’d gathered suffered the same failure.  I was rather unhappy and shoved everything in a box for another day.  I saved the pieces of the cartridge hoping someday to rebuild it, but I have yet to open the bag and release orange goo across my desk.

A few months ago, a fellow in the Facebook Apple II Enthusiasts group reported that he had contracted with an overseas manufacturer for a small run of new color ImageWriter II ribbons.  A few dollars and a short while later, I’m finally printing in glorious color with the unmistakable “dot matrix buzz” audible at the far end of the house.  I created a card and flyer with Print Shop GS, although the recipient doesn’t properly appreciate the origins.

It’s a small and simple accomplishment, but there’s something satisfying about a working ImageWriter II.  Sure, I love fancy hardware like mass storage and accelerators, but I neither expected to own those “back then” nor knew anybody who owned those.  The lowly printer was the item that everybody seemed to own and was the missing piece in my idea of a “complete” system.

iwii

ImageWriter II: It prints in glorious color and is audible across the house. No system is complete without one.

LCSI Sprite Card

Next in my ongoing effort to document the world’s most expensive version of Logo for the Apple II, LCSI’s Sprite Logo for the Apple II Family, I show the included hardware sprite card.

The board is a custom design from LCSI based on the TI TMS9918A video display processor, a video chip used in several personal computers contemporary with the Apple II.  Most of the board area consists of the standard TMS9918A chip and support circuits, including 16 KB of video memory (U1 – U8), the video clock, and the composite out.

A short pigtail brings the composite video connection to the outside of the computer case.  The sprite card does not display normal Apple II video, and the user must switch the cable between the sprite card and normal video output when switching between software designed for the card and other software.  There’s a separate ground lead from the composite connector to the power supply.  I’ve never seen a similar separate ground lead on any other peripheral card.  Perhaps LCSI had trouble passing the FCC tests and added this ground as the least expensive fix.

This card includes a 2 KB EPROM.  A ROM (or EPROM) allows reliable software detection of the card.  However, 2 KB is too large for this function alone.  Since the 64 KB main memory of the Apple II is limiting for Logo, I expect the designers used the extra space for Logo-related code or data.  I’ll examine the contents in a later post.  There’s a second unpopulated (U14) ROM footprint.  Perhaps LCSI considered using lower density EPROMs or more EPROM.

The decoupling capacitors (C1 – C10) are too large for the PCB footprints.  Notice how the leads are bent at odd angles to make the available parts fit.

There are two unplated holes (one near C13 and another near U1) in the PCB.  I have no idea why these exists.  Perhaps they’re mounting holes used during manufacturing, or perhaps they’re harmless errors in the board design.

I look forward to seeing the card “in action.”

Mold Making and Casting

I joined the Mold Making class with the Central Oregon Makers last week.  Before going, I had no idea how to make a mold or what I might use it for.  Although 3D printing (“additive manufacturing”) gets most of the attention, mold making and casting seem like useful and versatile tools for duplicating and fabricating items.  I could see using this technique to repair or replace small latches, wheels, key caps, housings, and decorative features where an original is available.  For example, I’ve had trouble finding robot wheels I like, but now I can make my own.

It’s nice to have another tool in my toolbox, and I expect to invent problems just to use this tool.