Boot address can be either depending on the disk card used.
Single density is E900, double is E800 (more rom). However all
of single denisty cards also respond to E800 so E8000 always wins.


If the ram stops at 7fffh then you have a address bus problem
either a short, or the bus driver on the CPU card is cooked.

Maybe you only have a 32K card!

Allison


--- In NorthStar_Computers@yahoogroups.com, Chuck Magee
<chuckcmagee@...> wrote:
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> Hmm, the boot address is supposed to be E900, not E800!
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> To: NorthStar_Computers@...: billdeg@...: Sat, 3 Jan 2009 15:04:30
+0000Subject: [NorthStar_Computers] N* Horizon Project Update -
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> I had written a while back looking for a processor card. I got
onefrom Bill S (I think he may be a member of this group?) Anyway,
hereis a project update. This is a work in progress.1) Not getting 5V
to the A drive (less than 2V). Traced the problemto the 7805 inside
heatsink, 6030B, the front-most 7805. I replacedthe 7805 and now I get
the correct voltage to everything.2) I checked every card, they all
seem to be getting the correctvoltages (12 or 5) ZPB processor (also
have a ZPB-2)MDS-AD3 (also have a MDS)IMS 4mhz 16K RAM set for top
memory (I believe - checking to confirm)N* 16K RAM bd (8000-Bfff)n*
32K RAM bd (0-7fff)3) I installed an in-circuit z80 emulator to check
the memory (read /write test) - no errors through 7FFF. I can't write
to anything abovethat, but the RAM is there, unsure why but I assume
that this is partof an initial lockdown of RAM by design, as part of
the bootstrapprocess (I have to confirm this). I checked location E800
and whatappears to be bootstrap code is located in this location
(which iswhere the manual says it should be). I don't at the moment
have acopy of the bootstrap code, but I assume I can find this on the
web toconfirm it's loading into memory. Looking for that now.4) When I
power on the machine, both drives spin but neither engagethe boot
disk. After maybe 20 seconds the drives stop spinning. Iverified that
the drive dip switches were correct from when the systemworked. I also
tried other similar drives (using Tandon 100-2A's). It's possible that
I have the wrong settings,. but this is what workedbefore:A DRIVE:
Tandon 100-2A jumpering TP11's 1st and 3rd (facing from thefront) and
inserting a T-RES terminator in TP7B DRIVE: MPI model 52 with G
jumpers on: 2-5-7, terminator installed.I must be getting close. I
will let you know if I make more progress. Bill
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