Interest in a PDP-8/e/a/f/m 32K RAM kit?

I will commit for for three. Dave On Tuesday, March 4, 2014 9:28 PM, Vincent Slyngstad <vrs at msn.com> wrote: Various replies to various comments... > >From: Pontus Pihlgren: Tuesday, March 04, 2014 11:09 AM >> It is tempting at that price point. >> >> With risk of increasing the price, wouldn't be nice to include Philipps >> "OmniUSB" in the design? There is plenty of room for it. > >One of the constraints of a hardware Kickstarter, which I can >agree with in principle, is that there must exist a working >prototype.? So, my PCB will be based on a drawing of Steve's >prototype, without substantive change.? That also effectively >rules out FRAM, etc.? My drawing does include lots of >prototype area, though, just like Steve's prototype. > >On Mar 4, 2014, at 2:20 PM, Alan Hightower wrote: >> Most people I know who restore old machines, including me, have >> an irrational disdain for batteries. > >As Tony has pointed out, one needn't, and probably shouldn't, >put the batteries near anything important.? I've laid the board >out like Steve's prototype, with the circuitry near the edge >connectors, and the battery near the handles.? If that's not >far enough away, then there is Tony's suggestion of a cable >and a box :-). > >From: David Riley: Tuesday, March 04, 2014 1:03 PM >> As far as the bus transceivers, it looks like he's using 26S10 >> ICs, which are at least still actively sourced by TI. > >I want to be clear that this is Steve's design, not one of mine. >While mine typically do use the 26S10, Steve's gone a different >direction, which he nicely describes on his page.? His design >has the distinct advantage of a working prototype. > >From: Eric Smith: Tuesday, March 04, 2014 1:22 PM >> There's a reason DEC specified the Vih of 1.4V, which is that on a heavily >> loaded bus it's entirely possible for a valid logic 1 to be that low.? In >> 1983 I tried to debug a large 8/e system which had been donated to a >> community college after years of service controlling the scoreboard at >> Kauffman Stadium. I often saw the logic 1 on the bus signals lower than >> 1.6V. > >Without getting into the whole can of worms about bus driver >choices, the prototype works, and that's a big deal.? Maybe it >doesn't work if you move your DMA device to the other end >of a 20 foot ribbon cable -- I doubt that's been tested.? On >the other hand, you shouldn't need to put it there, as this >thing potentially frees up a lot of slots.? I should say that >only the memory pins, not the whole Omnibus, are playing >fast and loose here, and the only devices connected to those >should be CPU, memory, and maybe a DMA device.? (Does >anyone actually put more than one data break device on >their Omnibus?) > >From: Alan Hightower: Tuesday, March 04, 2014 5:05 PM >> FYI, a normal ENIG finish is very thin.? Most board houses will charge >> extra for hard gold fingers which are designed for insertion durability. > >These boards would have proper gold edge connectors, silk screen, >and solder mask, plated through holes, etc.? I've had some experience >with the board house, and their stuff has always been great. > >> 4 layers is not necessary as most signals on the bus transition or are >> registered sub 1 MHz. > >Agreed.? These would be 2 layer boards, with 16 mil signal traces, 32 mil >power and ground traces (well, battery power is 16 mil), and a fair amount >of polygon area for power and ground as well. > > >? ? Vince? > > >