I've developed a Woz Machine based floppy disk controller for the Apple-1, which was subject of this April Fool's joke:


Here is a photo which shows the ICs and the functional sections:

Uncle Bernie's Floppy Disk Controller for Apple-1

These are the parts functionally identical to Apple's Disk II card:

7405 - "Glue Logic"
74LS74,74LS299,GAL16V8/PAL16R6 - "Woz Machine"
74LS259 - "Soft Switches"
74LS132 (1/2 of the IC) - "Drive Select"
555 - "Motor Timer"

These are the Apple-1 specific additions I had to make:

74LS132 (1/2 of the IC), 74LS123 - "Clock Generator"
GAL16V8/PAL16R4 - "TFC"

These additions are necessary because the Apple-1 does not have a 2 MHz "Q3" clock on its bus, which clocks the Woz Machine, so the "Clock Generator" makes a substitute from the 1 MHz system clock. And the "TFC" is where the magic happens to make the whole thing work under the constant barrage of non-transparent DRAM refresh cycles, which steal CPU cycles and break Woz' original concept based on precise CPU cycle counting in all the timing critical RWTS routines.

As far as I can say 6 weeks into the development of the new RWTS routines, it does work, and it does work reliably. The "TFC" makes all the trouble with the stolen CPU cycles go away, like a Stage Magician makes all sorts of things, animals and even beautiful girls disappear in front of your eyes. True "Magic" !

Any interest / questions ? - Feel free to ask and post your comments in this thread. The more responses this thread gets, the higher the chance that I don't just shelve this project after I have completed the RWTS.

P.S.: for the "purists" among us: only using year 1978 "period correct" parts was an imperative requirement in my Objective Specification for this project. MMI reveiled the PAL to the public in March 1978. It was a game changer ! TTL and LSTTL became obsolete over night, technically, but not commercially, since they had a market momentum too large to die out quickly. But technically, the PAL killed them dead. Apple released their Disk-II system for sale 4 months later, in June 1978. Do not get distracted by my use of those GAL16V8 ... these are only used to emulate the precious and horribly expensive bipolar PAL16R4 and PAL16R6, which are very rare nowadays. The GAL16V8 is based on EEPROM CMOS technology and came out in 1985. But unlike PALs, GALs can be edited to make changes to the logic within. This is why I use them for the development work.

P.S.S.: Another riddle for you (I'm the "Riddler" although I like "Iron Man" more): guess what the "TFC" stands for. Here is a hint: there is a movie about a close relative of this device having the same acronym but not exactly the same name. You can also guess the title of the movie. Try it ! Uncle Bernie's riddles always are fun ! Life without riddles to solve would be boring !

Ref : https://www.applefritter.com/content/uncle-bernies-woz-machine-based-apple-1-floppy-disk-controller

PDRM1281.jpg (8 downloads)