4 Oct
2007
4 Oct
'07
1:09 p.m.
Having got the Mitac A2 clone up and running (checked out the 80-column output
today and that was fine - only casualty in the whole machine was one cap that
had gone high-ESR), I've dug my Apple /// out of storage...
Disk ]|[ question - should the ribbon cable to the internal drive be plugged
into J2 or J3 on the drive's analog board (does it even matter)? A long time
ago I disconnected mine as a precaution; the drive began eating disks, but I
didn't have time to get to the bottom of it at the time - I suspect it just
needs a good clean.
I can't for the life of me find where I made a note of which socket the cable
plugs into. Normally I leave myself a note somewhere in the machine for things
like this, but for some reason I haven't with this one :-(
cheers
J.
7 Oct
7 Oct
10:57 a.m.
New subject: Apple ii disk controller again...
This item has been discussed recently, and I found myself figthing this
same floppy diskcontroller in my Lilith external floppydrive.
This is a 6502 subsystem with 4K rom/4k ram, a 9600 baud serial channel
( goes to the Lilith ) and said floppycontroller.
Symptoms :head goes to track zero, no directory is found.
I did not find a schematic on the net for this floppy controller.
When backengineering it I found that both Proms and the 74174 have their
power switched. Why would that be ? seems very hairy to me.
If anyone has such a controller and/or floppy drive available I'd be
interested. ( Switzerland )
Jos
1:56 p.m.
New subject: Apple ii disk controller again...
Symptoms :head goes to track zero, no directory is
found.
I did not find a schematic on the net for this floppy controller.
IOf this is a standard Apple Disk// controller, there's a schematic (and
indeed a schematic of the disk drive analogue board) in Appendix E of the
Apple DOS manual. I have no idea if that's availale on the web, I have a
paper copy in front of me.
When backengineering it I found that both Proms and
the 74174 have their
power switched. Why would that be ? seems very hairy to me.
Yes. This was a typicval Apple method of saving power. No matter that
it's a made idea to paply logic signals to an unpowered chip. And people
wonder why I dislike Apple hardware designs...
The state machine ('174 and the P6/P6A PROM) is enabled by the motor-on
line The boot ROM (P5/P5A() is eanabled from the IOSEL/ signal on the
edge connector, which also enables said ROM.
Is there anything I could easily type (pinouts of the slot, pinouts of
the drive cable, etc) that would help you?
-tony
8:33 p.m.
New subject: Apple ii disk controller again...
No matter that it's a [bad] idea to [apply] logic
signals to an
unpowered chip.
I recently built a ROM reader with a parallel-port interface.
But it had one bizarre problem: the last byte of the ROM always read as
FF. I finally tracked it down. I'd connected Vcc, and I had tied the
enable signals on the ROM together, to the ground pin - but hadn't
connected the enable-and-grounds anywhere. As long as at least one
input was low, it powered the chip through the protection diodes (thank
the TTL, and TTL-alike, output current-sinking capacity when low),
which was why the rest of the chip read correctly - but as soon as all
inputs were high, the outputs perforce all showed high too. (The time
between address line setting and data line reading was in the
microseconds, plenty of time for ROM power-up.)
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8 Oct
8 Oct
2:23 a.m.
New subject: Apple ii disk controller again...
Tony Duell wrote:
Looked some more and it seems that power switching is done to stop a
PROM output being shorted by a 74ls05 output !
i.e. An input ot the 74ls323 is either driven by the Stateprom, or
pulled low by the ls05 . That is indeed two outputs being shorted.
And this is supposed to be a clever design....
When
backengineering it I found that both Proms and the 74174 have their
power switched. Why would that be ? seems very hairy to me.
Yes. This was a typicval Apple method of saving power. No matter that
it's a made idea to paply logic signals to an unpowered chip. And people
wonder why I dislike Apple hardware designs...
Is there anything I could easily type (pinouts of the
slot, pinouts of
the drive cable, etc) that would help you?
Thanks, meanwhile the problem has been traced, with a bit of luck, to a
bad connection between 2 pcb's in the floppydrive itself. I was able to
copy Kermit across and am now happily downloading my second Lilith disk.
Jos
3:02 p.m.
New subject: Apple ii disk controller again...
Tony Duell wrote:
Looked some more and it seems that power switching is done to stop a
PROM output being shorted by a 74ls05 output !
i.e. An input ot the 74ls323 is either driven by the Stateprom, or
pulled low by the ls05 . That is indeed two outputs being shorted.
FOrutnaely it's not quite as bad as that. That '05 (section d if my
schematic is right) holds the S0 input of that '323 in a defined state
when the state machine isn't powered. Why, I am not sure :-). But that
'05 is driven by the power switching signal, there's no possility of a
contention. It's pulling low an output pin on an IC that's grounded but
not powered.
When
backengineering it I found that both Proms and the 74174 have their
power switched. Why would that be ? seems very hairy to me.
Yes. This was a typicval Apple method of saving power. No matter that
it's a made idea to paply logic signals to an unpowered chip. And people
wonder why I dislike Apple hardware designs...
And this is supposed to be a clever design....
Many times I'ev crtiicised the Apple ][ design and been flamed for it. At
least you realise why I think it's a right kludge from start to finish!.
-tony
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