4 Mar
2014
4 Mar
'14
7:21 p.m.
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