3 Jan
2012
3 Jan
'12
2:32 p.m.
Date: Sat, 31 Dec 2011 13:24:36 -0800
From: Josh Dersch <derschjo at mail.msu.edu>
Subject: Re: Looking for 8080/Z80 BASIC
On 12/31/2011 12:15 PM, MikeS wrote:
----- Reply:
> Just curious:
> Does your memory configuration support swapping out the RDOS boot/monitor
> ROM?
Not at the moment, I haven't quite worked out if
this can be made to work
properly with non-Cromemco memory boards. The 64FDC manual suggests
"Set[ting] the switches on the RAM board(s) so that memory from 8000h to
FFFFh is disabled..." which implies that the boards must support some way
of re-enabling the memory via software (for when the FDC's ROM is disabled
via a write to port 40h).
I'm wondering if this board isn't really
optimal for this setup -- it
seems very geared toward having a complete Cromemco setup, which I do not
have.
----------------
I don't see why it would be a problem; the RDOS boot/monitor ROM lives at
C000 so it should work with 48K RAM even if you don't disable it; ISTR that
some folks simply connected the ROM chip select to the Phantom line if they
had non-bankable memory and wanted to switch it in and out. And of course
the ROM can be completely disabled as well.
It controls up to four total 5.25 and/or 8" drives with write precomp, has
an RS-232 console port and a pretty good monitor with the usual memory and
disk manipulation, some basic diagnostics, etc.; not a bad card IMO. And
it's fairly well documented.
----------------
For right now, I was just planning on assembling a raw
binary image and
using a PC (with a bit of hacked together software) to push the image into
the IMSAI's memory via the 64FDC's serial port, using the onboard monitor
commands. Just for fun :).
If you know of a source for images of these
third-party CP/Ms, let me
know. Dave Dunfield's site has a CP/M for the 16FDC, which as far as I
can tell (from a cursory glance at the manuals) has identical I/O port
behavior to the 64FDC so I may just be able to use that, assuming I can
write the 8" image to a 5.25" floppy.
----------------
As a matter of fact Dave also has a utility for the FDC that actually lets
you create a bootable disk over the serial port.
No big difference between the 16FDC and the 64 FDC; mostly just stuff added
for later models of 8" drives (Tandon 848) and mods for the tape drives.
mike
4 Jan
4 Jan
10:40 a.m.
A simple implementation, done at the time, was to tie the
RDOS ROM chip enable pin to the S-100 PHANTOM line with a
diode. I have both 4 and 16 FDCs modified that way and it
works very well.
Bill S.
7:24 p.m.
New subject: Cromemco FDC
On 1/3/2012 2:32 PM, MikeS wrote:
Date: Sat, 31 Dec 2011 13:24:36 -0800
From: Josh Dersch <derschjo at mail.msu.edu>
Subject: Re: Looking for 8080/Z80 BASIC
On 12/31/2011 12:15 PM, MikeS wrote:
Actually, the board occupies everything from $8000 on up, if the manual
is to be believed ("The 64FDC appears on the S-100 bus as a 32K memory
card..."). Since the ROM is at most 8K in size that's a bit suboptimal
:). (And it starts at C000 for apparently arbitrary reasons...)
----- Reply:
> Just curious:
> Does your memory configuration support swapping out the RDOS
> boot/monitor
> ROM?
Not at the moment, I haven't quite worked out
if this can be made to
work
properly with non-Cromemco memory boards. The 64FDC manual suggests
"Set[ting] the switches on the RAM board(s) so that memory from 8000h to
FFFFh is disabled..." which implies that the boards must support some
way
of re-enabling the memory via software (for when the FDC's ROM is
disabled
via a write to port 40h).
I'm wondering if this board isn't really
optimal for this setup -- it
seems very geared toward having a complete Cromemco setup, which I do
not
have.
----------------
I don't see why it would be a problem; the RDOS boot/monitor ROM lives at
C000 so it should work with 48K RAM even if you don't disable it; ISTR that
some folks simply connected the ROM chip select to the Phantom line if
they
had non-bankable memory and wanted to switch it in and out. And of course
the ROM can be completely disabled as well.
How does the "phantom" line work? I see references to this in some of
my S-100 manuals but I'm not clear how it works (who raises/lowers it,
when, etc...)
It controls up to four total 5.25 and/or 8" drives with write precomp,
has
an RS-232 console port and a pretty good monitor with the usual memory
and
disk manipulation, some basic diagnostics, etc.; not a bad card IMO. And
it's fairly well documented.
It is pretty nice, the documentation is fairly decent (though seriously
lacking in documentation of error codes as I'm finding while trying to
get it to boot a floppy :)).
Thanks for the help!
- Josh
8:20 p.m.
New subject: Cromemco FDC
Josh Dersch wrote:
How does the "phantom" line work? I see
references to this in some of
my S-100 manuals but I'm not clear how it works (who raises/lowers it,
when, etc...)
It can be a little bit "implementation dependent" but usually there are
cards that assert phantom (it is active low, there has to be a pull up
on it somewhere (the CPU card I think)) and cards that "honor" phantom.
When an address is presented to the bus, any phantom asserting card that
whishes to override that address pulls the phantom line low. A phantom
honoring card that would normally respond to the address will instead
suppress any activity. Note that this system does not prevent multiple
phantom asserting or phantom honoring cards from stepping on each other.
Careful system configuration is still the responsibility of the builder.
In the case of the Cromemco FDC cards, the FDC becomes a phantom asserter.
Any RAM card that the system has that resides in the same address space
($C000-$CFFF in the case of a 4FDC) must honor phantom. The CPU presents
an address to the bus, the FDC card does an address decode, determines that
it is an address it wants to respond to and activates the ROM (the CE (chip
enable) pin on the ROM is also active low) asserting PHANTOM at the same
time, disabling the RAM card. When you deactivate the RDOS ROM with the
poke to the I/O address, then the FDC card will no longer activate the ROM,
PHANTOM will no longer be asserted and the RAM card will respond to the
address previously occupied by RDOS. I run CDOS in a full 64K
configuration this way.
Bill S.
4740
days inactive
4742
days old
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