20 May
2002
20 May
'02
6:29 a.m.
From: "Erik S. Klein"
<classiccmp(a)mail.vintage-computer.com>
---snip---
split octal stuff cut because already answered.
---snip---
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.
You'll need to check to see if the address is getting
driven to the bus with a meter, logic probe or 'scope.
It may just be a bad LED or driver on the panel,
it may be a bad switch or some other part of the cicuit.
Why would the data lights ever show anything but on or off?
I sometimes get dim glows from the data LEDs.
When the code is running, they blink faster than your eye
see. They may appear dim when toggling fast.
What data can I expect to be in the RAM on boot-up? Is this
answer different for Static vs. Dynamic RAM?
You can't depend on boot up data in either. Most DRAMs
will boot with alternating 00/FF data. Sometimes these
are in blocks. Most statics tend to be more ramdom but
sometimes look similar in patterns to the DRAM. If you
don't know if there is RAM at a location, use the
front panel controls to change values. If there is RAM
there, it will hold the new value you wrote.
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?
I have a IMSAI but I suspect the sequence would be similar.
STOP-RESET-EXAMINE-RUN, w/ address switches set to the
boot address. If you do have a panel problem and can't
get the address loaded properly, you could put a simple
JMP into some RAM that you can access. Toggle in
the JMP XXXX and then set the address switches to the
JMP instruction and do the EXAMINE-RUN sequence.
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.
I have EPROMs that are over 20 years old that are still
holding data. The boot sequence is quite small and it is
unlikely to be bad. From what you said earlier, I would
suspect that the main problems may be incorrect switch
settings or problems with the fron panel.
Dwight