On 10/25/16 12:10 PM, Guy Sotomayor Jr wrote:
On Oct 25, 2016, at 8:38 AM, allison <ajp...@verizon.net> wrote:
On 10/25/16 10:02 AM, Guy Sotomayor Jr wrote:
On Oct 24, 2016, at 11:35 PM, ben <bfranc...@jetnet.ab.ca> wrote:
On 10/24/2016 2:18 PM, David Bridgham wrote:
On 10/24/2016 01:37 PM, allison wrote:
The voltages are based on TTL levels. What are the unique voltages?
The QBUS spec from the 1979 Bus Handbook (the Unibus levels are the same):
Input low voltage (maximum): 1.3 V
Input high voltage (minimum): 1.7 V
And from the TI datasheet for the 74LS74:
Vil - low-level input voltage 0.8 V (maximum)
Vih - high-level input voltage 2 V (minimum)
So no, the DEC bus voltage levels are not TTL levels. Yeah, TTL might
work on a smaller system but you can see that if you push it out to its
limits, TTL could start getting flaky. That's the kind of bug I'm happy
to have DEC's engineers figure out and not have to track down myself.
But who has the big systems now days? The days of 4K core is long gone.
Use TTL and try to keep the systems small.
I just posted what one of my systems is (11/40). It has 128KW of core which
takes 4 9-slot backplanes. I have a fair amount of I/O on that system so I
have 2 BA11F chassis *full* of backplanes (each BA11F holds 5 9 slot
backplanes).
My other large system is an 11/70 with a BA11K as an expansion box. The whole
point of Unibus was to allow for large configurations.
And I can guarantee you that TTL will *not* work in those systems.
Maybe if care is not taken. Again there are TTL part and those designed for
bus use.
Bad choice, bad results. I've seen a few like that that broke even with DEC
parts.
That’s why there’s the UNIBUS spec that DEC published. In big systems, you must
follow the guidelines even with the proper transceivers. Sometimes it requires
that
things be split up and cable length added.
Also, I think in a previous email you mentioned that the UNIBUS is 240ohm.
It’s not.
It’s 120ohm.
My book says no. Qbus is for sure 120.
Then again My 11/73 is BA11S and Ba11N both with 18 slot 4mb ram (two cards),
DELQA,
two RQDX3 (one for RX floppies, second for RD disks), RLV21 (in box2), CMS scsi,
RXV21V-RX02, DZH11V and Parallel IO (ttl) in box 2 and Gigilo card (DEC sound
card for Qbus) in Box 1. Likely a few IO I forgot.
OK, it’s still a small system by UNIBUS standards. ;-) I can’t check either
my 11/40
or 11/70 but (from memory) the configs are:
11/40:
BA11F(1): CPU with all options (including FIS), 2 32KW core memory, additional
backplanes to fill it up
BA11F(2): 2 32KW core memory, 1 RK11D (4 slot backplane), additional backplanes
to fill it up
The “standard” Unibus devices as I recall are (there are more as most of the
backplanes are full):
4 DL11s
DZ11
RL11
At least one tape drive interface of some sort
bootstrap/terminator
BC11A-15 to connect the two BA11Fs together.
11/70:
BA11F(1): CPU with all options, Hypercache (4MW option that looks like a 4MW
cache to the CPU), 2 SMD controllers that plug into the slots for the massbus
controllers (4 slots each). 2 Massbus controllers (4 slots each), 1 DL11
BA11K: RK11D 4 slot backplane, 2 RL11 controllers, TS11 controller, TU81
controller, 2 DZ11s, 3 DL11s, 1 ethernet controller
There’s more on this system, I just don’t recall it all at the moment. Again,
this system is *full*. I’m at the point where if I want to add more stuff I
need to add another BA11K.
bootstrap/terminator
BC11A-15 to connect the BA11F to the BA11K
By all DEC standards its unsupported config. Bus signals still look good.
Mine has many LS24x part and 7438s as there are more than a few IO cards
that are non DEC (mine).
Example IO a PIO IDE interface test dog wire wrapped (usually the worst)
alone with A/D and D/A.
By Qbus standards its a monster and it was rare to see more than two
boxes and usually the cages were
not the 18 AB slot but the 9 slot ABCD configuration. Runs unix well
and usually that breaks machines
that are flakey. Also Qbus uses 120 ohm termination so the drivers have
to sink more current.
Never could fake the DEC interbox cables, those are well done to work right.
The BA123 uVax also has a few odd cards, doesn't seem to care. THose
however were not fast
on the bus as they used PMI for Memory.
Another example is the 11/23 with all heathkit cards for memory, IO and
a few unique homebrews.
I've never seen a bus level issue die to devices used.
I've seen my share of BIG VAXen with many unibus crates too.
Yes, and they all used the proper UNIBUS transceivers and not TTL parts.
mostly.... A few of the systems were not production and engineering did
play.
Bottom line is someday there will be no DEC parts and what then? I
reserve DEC parts
for repairing defunct boards for new and unique build it would be a
waste of scarce
material. The vector interrupt chip DC-series is one that is hard to
fake without a
larger number of chips.
For preservation reasons its very important, for hacking an old system
not as much.
In my collection I have both.
Allison
TTFN - Guy
