More PDP 11 hacking (help!)

From: Pete Turnbull <>
Date: Tue Feb 8 03:02:07 2005

On Feb 7 2005, 20:26, Vintage Computer Festival wrote:
> Ok, so I decided to go back to the generic LSI 11/23 system I first
> started with a few weeks ago.

> I'm now getting a prompt! Yah!
> Not only that, I'm getting the disk controller bootstrap ($) prompt!
> Yah!
> But now are new woes: when I type in "DY" to boot off the DY drive
> system pauses for a split second and then dumps into ODT with 165426.
> Looking at that address shows that there's no code there.

No code, as in ODT gives an error (prints a "?" and a carriage return)
or it's zeros?

> If I issue 173000G or 773000G, I get back to the $ prompt. Ok.
> However, one thing I noticed is that now, location 0 now has code!
> Or at least, something is there. If I clear the first dozen or so
> and then reboot, the zeroes are overwritten. The weird thing is that
> don't see the drive light going on or the head relay engaging.

Apart from the lack of drive activity (LED flash and the clunk from
head relay) it sounds like you haven't got a bootable disk. Or that
you have, but it's for a different controller (a DX-bootable disk will
not boot on a DY, nor vice-versa).

> I've tried the system with both the DSD and RXV21 controllers with
> different sets of drives and I basically get the same results.

> No matter whether I boot with DY or DY0 or DY1, it always breaks into
> at 165426.

Depends on what's at location zero. You could try entering a copy of
the normal RX02 bootstrap code at location 1000 and stepping through it
to see what happens and where it goes wrong. Did you know that you can
type "P" instead of "G" to make the processor restart at the last-used
address, without resetting the bus and devices on it, and that you can
do this with the HALT switch on, so it single-steps? So if enter a
manual bootstrap at 1000, set the HALT switch, type "1000G" and then
keep typing "P" you'll single-step through the code starting at 1000.

Pete						Peter Turnbull
						Network Manager
						University of York
Received on Tue Feb 08 2005 - 03:02:07 GMT

This archive was generated by hypermail 2.3.0 : Fri Oct 10 2014 - 23:37:36 BST