25 Oct
2016
25 Oct
'16
7:02 a.m.
On Oct 24, 2016, at 11:35 PM, ben <bfranchuk at
jetnet.ab.ca> wrote:
On 10/24/2016 2:18 PM, David Bridgham wrote:
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.
If you want to build boards that will work in a small subset of systems that?s
find?but don?t advertise it as Unibus compatible. I test the boards I produce
in all of my systems (11/20, 11/34, 11/40 and 11/70) and they all use DEC bus
interface chips.
TTFN - Guy
On 10/24/2016 01:37 PM, allison wrote:
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. 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.