Great work Brian, Looking at the photos makes me wonder if something like this would be possible for the 8201A as a 3rd bank 32k expansion slot. With the size of components being drastically smaller, And internal plug in might be possible. Just a thought.
I don't own a WP-2 but I am familiar with it. Great work on expanding its capabilities. Kurt On Mon, Oct 19, 2020, at 12:08 PM, Brian K. White wrote: > On 10/15/20 10:13 AM, Josh Malone wrote: > > That sounds awesome, Brian! I'm excited to build one of these once the > > PCB is ready. Is the flash version able to be written by the WP-2? Or > > is this just for running z80 programs on the WP-2 which you flash > > externally? > > > > -Josh > > > > On Thu, Oct 15, 2020 at 12:45 AM Brian White <[email protected]> wrote: > >> > >> The last piece I as waiting for came in today and the ram card works both > >> mechanically and functionally. > > > Ok finished the next round of iterations on these WP-2 expansion cards. > Now waiting for the boards to come it to verify it's all still good. > > Lot's of cleanup and a couple new boards. > > Now there 3 main types of cards and a programing adapter. > > v003_RAM - is a 128K SRAM board that snaps into the 3d-printed carrier. > It has a cap, resistors and a diode to provide backup power for about 10 > minutes. > > v004_RAM_B - is a large board that fills the slot itself instead of > using a 3d-printed carrier. It has the same 128K SRAM and cap as > v003_RAM, and also adds a coin cell battery, which should preserve the > memory for about 10 years vs about 10 minutes. The cap is still there > mostly because "why not?" and it allows you to change the battery > without losing the contents. > > v003_ROM - is a 128K or 256K "ROM" (flash) board that snaps into the > 3d-printed carrier, and only has a single pullup resistor aside from the > flash chip. > > programming adapter for the ROM board - simple pcb with a set of regular > 2.54mm pitch DIP pins on the bottom to go into a TL866 or similar, and > one row of 1.27mm pitch pins on the top which you stick the ROM board > onto to program it. > > https://github.com/bkw777/WP-2_IC_Card > > I could use help making less naive backfeed prevention and reverse > polarity protection circuits on the two ram boards.. > > On the regular ram board with only a cap, no battery, I don't need to > worry about reverse polarity, just backfeeding from the cap to the WP-2 > VDD rail when you turn the WP-2 off with the card plugged in. > > Right now I just have a Schottky diode between the the WP-2 VDD and the > rest of the card. This drops the working voltage on the card from 5.1v > to 4.7-4.8, which drops the run-time of the cap. This isn't *so* bad, > but I believe something better can be made without getting too crazy > with too many parts. On this board the diode just handles the case when > you turn the machine off with the card still plugged in. If you just > pluck the card out while it's powered on, the cp alone (no diode) > preserves the ram for at least 10 minutes. That's not really long enough > to be good for much, but it is a good safety against accidents. The > power button is too easy to hit, so even a few seconds grace period is > worth having. Several minutes is way more than needed for accidents, but > not enough to say, pack up, drive home and download stuff later in the day. > > The real problem is the battery-backed board. > > I decided it really should have reverse polarity protection from the > battery holder. It's just too easy to put the thing in backwards. So I > added another of the same schottky diodes on the + from the battery. > This does double duty and also takes care of protecting the 3v battery > from the 5v active running power. But there, the small voltage drop > hurts more, because the battery is only 3v to begin with. That could > really benefit from a proper pmos circuit or maybe just an ordinary > switching or rf transistor? Or I can actually fit 2 battery holders on > the board to get 6v which I can then drop to 5, but I shouldn't have to > do that. > > But the simple diode circuit will at least work reasonably. It just > won't hold memory for as many years, but still "several" regardless. So > the battery-backed ram board should work like a nice removable "flash" > drive. > > Pics (renders), and viewable svg prints of the schematics all in the > readme on github. (link above) > > -- > bkw >
