Erik,
I used to have an Altair with the MITS disk drive system including the disk drive boot strap option. The boot strap option was a pair (IIRC) of 1702s in the MITS EPROM board. I looked the code in them and it's exactly the same as the boot strap loader that the disk drive instructions tell you how to toggle in with the front panel switchs so if all else fails toogle in the code that's shown in the DD manual. That way you can tell if your DD system is working or it the problem is in the BS loader EPROMs. I don't have the Altairs or manuals or anything else any more so that's all I can tell you. However it sounds like you've got problems with the front panel or ????.
Joe
At 07:51 PM 5/17/02 -0700, you wrote:
>Hello all,
>
>I am relatively new to vintage computing and this list,
>although I've been working and playing with computers for a
>long time. I am, however, a software guy and have only a
>little skill with or knowledge of hardware.
>
>I've recently acquired a pair of Altair computers (8800 and
>8800a) both equipped with the "88-DCDD" single 8" disk
>drives. Unfortunately, I am having various difficulties
>with these machines. Hopefully the answers to some
>questions will push me towards a better understanding of
>these systems.
>
>My main issue at the moment revolves around the EPROM cards
>that hold the disk boot loader (DBL) PROMs for these
>machines. The cards are Solid State Music “2K/4K” cards
>with 16 slots for 1702s. I asked the list about these cards
>before and have since obtained an assembly/instruction
>manual, but it is still unclear to me how these things are
>configured and addressed.
>
>There are four address switches which are supposed to
>address the board as follows (this is taken from the
>manual):
>
>Address:
>000 000 to 017 377 - All switches on
>020 000 to 037 377 - A2, A3, A4 on
>040 000 to 057 377 - A1, A3, A4 on
>060 000 to 077 377 - A3, A4 on
>100 000 to 117 377 - A1, A2, A4 on
>120 000 to 137 377 - A2, A4 on
>140 000 to 157 377 - A1, A4 on
>160 000 to 177 377 - A4 on
>200 000 to 217 377 - A1, A2, A3 on
>220 000 to 237 377 - A2, A3 on
>240 000 to 257 377 - A1, A3 on
>260 000 to 277 377 - A3 on
>300 000 to 317 377 - A1, A2 on
>320 000 to 337 377 - A2 on
>240 000 to 357 377 - A1 on
>360 000 to 377 377 - None on
>
>I see issues with this from the outset. First, assuming
>this is octal, the addresses past 160 000 are beyond the
>address space of the 8080 chip in the Altair (200 000 being
>64K). As well, the gap of 16k at 160 000 to 200 000 is
>either an error in the manual or something I am missing
>since I can’t imagine the binary progression of switches
>having that gap. How is this card addressed?
>
>I’ve tried examining my way through the memory areas that I
>think are supposed to be addressed into the EPROMs (based
>upon various assumptions) but I get results that have me
>confused. Answers to some of these questions might help:
>
>Why would the address lights on the Altair not properly
>correspond to the address switches being set? If I set the
>switches at 1110111000000000, for instance, when I reset
>then examine the light at A11 doesn’t come on (the lights
>show 1110011000000000) even though I know that LED to be
>functioning.
>
>Why would the data lights ever show anything but on or off?
>I sometimes get dim glows from the data LEDs.
>
>What data can I expect to be in the RAM on boot-up? Is this
>answer different for Static vs. Dynamic RAM?
>
>What is the best way to execute the boot loader should I
>locate it? Can I set the address switches to the proper
>spot and run or do I need to code a simple program that will
>“JMP” to the known address?
>
>Much of my confusion might stem from the EPROMs themselves
>since they may have been erased by time. I have a freshly
>burned set on order which may help.
>
>Please forgive my ignorance and this really long post.
>
>Thanks in advance,
>
> Erik
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Received on Sat May 18 2002 - 22:11:50 BST