> From: Seth Morabito
> 1. Halt the CPU and enter ODT
I'm too lazy to check to confirm this, but I strongly suspect DMA requests
don't get serviced while the machine is halted. If so, you could use the
following code fragment to avoid that:
0400 12737 MOV #400, @#174400
777 BR .
Start at 0400, let it run for a couple of seconds, then halt the machine
and look at 01000 and up.
I'm reverse-engineering the firmware of the IOC board of an Intel MDS
Series II (with the iMDX 511 IOC firmware enhancement kit, so it's the
same as early MDS Series III firmware, but possibly not 100% identical
to firmware of the later MDS Series III using the IOC-III).
The IOC uses an 8257 DMA controller, which was the predecessor of the
8237 as used in PCs. While it is mostly pin-compatible, the 8257
register map is a subset of nor compatible with the 8237. Not a
problem since the 8257 datasheet is readily available.
The 8257 mode register (output) and status register (input) are
register number 0x8 of 16. The data sheet says that A3 should be 1 and
A2..A0 should be zero to access those registers, as expected, and does
not document what (if anything) registers 0x9 through 0xf do. It's
possible that they simply mirror register 0x8.
In the MDS, the 8257 is I/O ports 0xf0 through 0xff, so mode and
status should be at 0xf8, and indeed sometimes the firmware references
those. However, the firmware also inputs from 0xfd, and writes to
registers 0xfb, 0xfc, and 0xff. The values read and written don't
seem to me to completely make sense if I make the assumption that they
are mirrors of 0xf8, and I can't imagine why the firmware author would
have used 0xf8 in some places and other port addresses in other places
if in fact they are functionally the same.
Intel published the source code of the ROMs for the MDS main processor
(8080 or 8085), but I've never seen source code for the IOC firmware.
Update as I was writing this up:
I just spotted a comment in the MESS driver by fulivi stating that
port 0xfd reads as 0xff and is used to detect whether the chip is an
8237 or 8257. If so, perhaps the 8257 either ignores input requests
>from 0xf9 through 0xff, leaving the bus tri-state, or possibly it
actually drives 0xff, and perhaps it ignores writes to 0xf9 through
0xff. I'll have to go back through the disassembly and study what that
would do; it didn't seem like just the writes to 0xf8 made sense, but
the other writes may have confused me.
Has anyone actually seen a Series II or Series III with an 8237 on the
IOC board? Perhaps the IOC-III uses the 8237?
I have a single CP/M 1.4 boot floppy that came with my IMSAI 8080 system.
It?s been a bit of an effort, but the system is now fully functional from a hardware point of view.
I?m now looking for SYSGEN and FORMAT programs (or any programs at all) for the Versafloppy 1 controller card.
I?m hoping these will allow me to get a backup of the floppy before it dies.
It?s already marginal, and boots only once in every 3 attempts, so whatever I do, I?m going to have to be very careful.
For more info, you can see my post of VCF about it here:
Cheers & thanks.
In my recent Qbus haul, I found two non-DEC memory cards:
1. NSC NS23D
2. Dataram 40903 Rev G
Both are fully populatd with 2MB (1MW) of 256Kb x 1 chips, and both
are configured for address 0.
I'd love to use both together in one of my systems, but I can't find
a scrap of documentation anywhere, so I have no idea how to configure
the base address of either card. Disappointing!
Does anyone have docs for either of these beasts?
So here's something interesting (but not in my line):
PDP8/E Interface Manual - 1970
The same seller has some other PDP-8 documentation (set of prints of some
sort, etc, etc).
Picked up a TI CC-40 and it?s much smaller than I expected. I thought it was going to be the same size as a TRS-80 Model 100. I mostly got it because I wanted to try out the BASIC on it so I could update the list of computers with BASIC in ROM that I started on Wikipedia.
As soon as I got it I popped in some batteries and turned it on, and I was able to enter a one line BASIC program and run it. Then I pushed the OFF key and since then it won?t boot up at all, it just gives me half a screen of black squares. Thinking maybe I had put partially dead batteries in it, I replaced them with fresh ones and same thing. I also pulled the batteries and tried powering it up from the DC input jack, still no go. When it?s stuck like this the OFF key doesn?t do anything and neither does the little reset button next to the spacebar.
I?ve looked around for a service manual and haven?t turned up anything. Did my RAM chips go bad? Did the ROM go bad?
Here?s a pic of the CC-40 and an M100 next to it for scale:
Follow me on twitter: @FozzTexx
Check out my blog: http://insentricity.com
So I'm not sure what we've got, here. The machine seems to have only one
memory board in it, so, just for grins, I decided to look at the online docs
on the 1900, and see if it needed memory boards in pairs.
The doc described the model 1905 and the model 1955 - both of which have a
"diagnostic/maintainence control panel", with lights and switches, which this
machine doesn't have. Although that may not mean that much - people started
getting rid of them because they cost too much, so maybe this is a later
model, without them.
They also have a cutout in the top panel for a large keyboard (see pictures
online of these model) which again this machine doesn't have (the cutout,
that is)... It does seem to have one less CPU card than one of the models
(forget which one) in the online manuals (CPU cards only go from A-H on this
unit, not A-J), and no, there isn't a missing CPU card, i) the slots are
numbered, and ii) there's no empty slot.
I looked all over it for a model/serial number placard, which would give the
model, but NSFL, couldn't find one. :-( It does have a large red placard
panel on the front which says 1900, so I'm pretty sure it's _some_ flavour of
Burroughs 1900, but... Anyone have any idea what this thing might be, exactly?