More PDP-11 problems
charlesmorris at direcway.com
Sat Dec 31 19:32:08 CST 2005
As I posted previously, the 26.667 MHz master clock oscillator had
failed on the KDF11-BA cpu (probably from rough handling). For now
I have a 30.000 MHz module from the junkbox. Looks like I spoke
too soon (I had the J17-18 always-ODT jumper installed so seeing
the ODT prompt was not a surprise). I don't know if this minimal
overclocking is causing my current problems though:
I have found two substantially different tables showing how to set
the CPU DIPswitches. KDF11-B Maintenance Manual (MM), and KDF11-BA
Users Manual (UM). The UM says I should have switches 1-8 set to:
1-On: CPU diagnostic
2-On: Memory diagnostic
3-Off: No DECNet boot
4-Off: Turn-key boot (sel. sw 5-8)
7-On: RL01/02 boot
I don't have the MM handy, it was .TIFF pages, but for the same
functions only switches 5 and 7 were On.
Anyway, using either table, the RUN light comes on briefly, then
with the RUN light off, state LED's=1111. Manual says 17 octal
means the CPU is not in power-up mode 2, but J18-19 is correctly
installed. I don't get any memory test messages or identifying
text either, just the ODT prompt.
According to the UM page 2-5, it looks like the internal boot
address of 173000 is being generated correctly, but if BHALT L is
being (incorrectly) asserted, the result is entry to ODT and a
halt. Which matches what I see happening.
If I set the front panel HALT switch and flip RESTART, the CPU
immediately halts with state LED's=0001 which is correct. So it
doesn't look like the HALT line is shorted to ground.
Also, I can examine memory using ODT at the boot EPROM address of
773000 and read the following:
I don't have a PDP-11 disassembler handy but that looks like some
kind of executable code, hopefully the bootstrap.
When I examine memory at 173000 it's all 1's (177777) but I can
deposit and read data correctly into locations there. Shouldn't
the bootstrap program be copying its code there? Again, if the
HALT line is being set for some reason, then the copy operation
can't take place... is that where I should be looking or am I
following a false trail?
Any help greatly appreciated.
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