On Jan 5, 16:34, Tom Leffingwell wrote:
> On Sat, 5 Jan 2002, Pete Turnbull wrote:
> I did find on the MSV11-L
> that X was connected to U. I'm not sure what U is for, but seemed to be
> grounded, so I removed it, which I assume set the address back to 0. At
> that point it started working.
Yes, U is the ground for V...Z (K is the ground for L...P). X-U (with all
other bank pins disconnected) gives a start address of 00100000 (32K,
decimal).
> How do I know whether or not I need to enable or disable I/O page
> setting? I haven't tried to enable it on the MSV11-L, although it was
> enabled on the MSV11-D before I removed it. What symptoms occur if its
> set wrong?
If you have any devices in the lower 2KW of the I/O page, you should
disable memory access to that area. If you don't, you'll get a conflict
when both the I/O device and the memory try to respond to the same address.
However, not many small QBus systems have I/O devices in that address
range (160000-167777). It's normal to leave the whole I/O page for I/O
devices, and disable memory in that area, though.
> > And that's the second thing. The MSV11-L doesn't use BBS7 for
everything
> > it decodes, so you have to set it according to whether it's in a 22-bit
> > system or an 18-bit system. If there's a jumper from R-T, it's set for
a
> > 2MW system. Remove it for 128KW systems.
>
> I did find out that I have the 22-bit KDF11-A, although I haven't checked
> the backplane yet. If the backplane is 22-bit, should put the R-T jumper
> in the M8059? Does it matter if I only have 128KW of memory?
I don't know; try it and see :-) I suspect if you set it to 18-bit mode
and use it in a 22-bit system, it will respond to multiple addresses. If
you set it to 22-bit mode and use it in an 18-bit system with no
termination on the upper 4 lines, it may respond to noise on those lines
and not turn on when it should. The bus signals are active low, so if
there's no signal they should float high and read as zeros -- but life and
bus systems are not always so predictable.
OTOH, if you have a 22-bit processor, it's easy to upgrade the backplane by
soldering four pieces of wire-wrap wire to bus the extra 4 address bits
(and upgrade the BDV11 if necessaary).
--
Pete Peter Turnbull
Network Manager
University of York
Received on Sat Jan 05 2002 - 17:50:48 GMT