30 Oct
2025
30 Oct
'25
7:39 a.m.
Anyone here familiar with programming the 11/23 (KDF11-A) in assembler,
bare metal?
I have been trying to get a very simple test program to run on it but it
keeps halting on
an address outside of the program. Seems to always be the same address
which is why
I am thinking I must be missing something. The program runs fine on an
11/23+ or 11/70.
Below is the listing:
1 000000 .asect
2 014000 .=14000
3 014000 012706 002000 start: mov #2000,sp
4 014004 000240 loop: nop
5 014006 000776 br loop
6 .end
I have a hardware 11/23 but for convenience I have been testing on a SIMH
11/23 by
loading the binary from the simh prompt and then jumping to the start
address.
I have tested the same code on 11/23+ and 11/70 CPUs and it runs fine.
I am working in Linux and am using the following Macro11 cross-assembler:
macro11 - portable MACRO11 assembler for DEC PDP-11
Version 0.8 (07 Jul 2022)
Copyright 2001 Richard Krehbiel,
modified 2009 by Joerg Hoppe,
modified 2015-2017,2020-2021 by Olaf 'Rhialto' Seibert.
I then use the obj2bin.pl utility by Don North to convert from object
format to binary load format.
The following is what happens:
PDP-11 simulator Open SIMH V4.1-0 Current git commit id: 29d39002
sim> set cpu 11/23
sim> load test.bin
sim> g 14000
HALT instruction, PC: 005271 (HALT)
sim>
Am I missing some initialization parts or something? I have looked through
various manuals and
the processor handbook for the LSI-11 but if it is in there, I am missing
it.
Any pointers would be greatly appreciated.
-Peter
On Tue, Oct 28, 2025 at 3:38 PM Peter Ekstrom <epekstrom(a)gmail.com> wrote:
Wayne, Warner, Glenn,
Thank you very much for your responses!
Wayne,
I took a look at the PDP11GUI files and it is quite complex. I setup the
GUI on a PC here and tried it against my PDP-11/23 but wasn't able to get
it to work.
Not sure what I did wrong but I am definitely keeping it, and will go
through that source a bit later. I'm sure I'll learn a lot from it. Thank
you for the tip!
Warner,
Right now I prefer assembler because I am trying to learn more about it.
But I glanced at the BSD loader in C and find it quite interesting. I am
going to go
though that too a bit later. Thank you for this tip as well!
Glen,
I did look at the sources you mentioned and they were a bit more
bite-sized. So I have tinkered with it and am actually able to use it to
boot an 11/23 in SIMH
using that code. I have also cobbled together a little boot menu and
incorporated this loader there. Thank you for those pointers!
Thank you all!
-Peter
On Tue, Oct 28, 2025 at 6:38 AM Glen Slick via cctalk <
cctalk(a)classiccmp.org> wrote:
(DU) MSCP UDA50(RAxx) disk:
https://ak6dn.github.io/PDP-11/M9312/
https://ak6dn.github.io/PDP-11/M9312/23-767A9/23-767A9.mac
https://ak6dn.github.io/PDP-11/M9312/23-767A9/23-767A9.lst
On Mon, Oct 27, 2025, 4:48 PM Wayne S via cctalk <cctalk(a)classiccmp.org>
wrote:
Maybe look at pdp11gui ?
I think it downloads a boot loader so the code may be there.
<https://retrocmp.com/tools/pdp11gui>
PDP11GUI<https://retrocmp.com/tools/pdp11gui>
retrocmp.com<https://retrocmp.com/tools/pdp11gui>
[favicon.ico]<https://retrocmp.com/tools/pdp11gui>
Sent from my iPhone
On Oct 27, 2025, at 15:58, Peter Ekstrom via cctalk <
cctalk(a)classiccmp.org>
wrote:
I am looking for the assembler listing for a bootloader for booting
from
MSCP disks like RD-disks.
Google has not been very helpful and my assembler knowledge is not
enough
for me to write one from scratch. Does anyone
have one they can share?
- Peter