Re: On attempting to make the 3.5" floppy adaptor to work...

[Tristan Mumford <xtristan.xmumford@xgmail.xcom>]

Michael J. Mahon wrote:

> Tristan Mumford wrote:
>> Michael J. Mahon wrote:
>> 
>> 
>>>Tristan Mumford wrote:
> 
> <snip>
> 
>>>>I also managed to turn an 18f452 into a nice heating element. When I did
>>>>the reshuffling I managed to short the -12v to one of its IO lines,
>>>>which would have resulted in a nice 17v potential difference inside the
>>>>chip. Or is it 16v. Doesn't matter anyway. Now I have something to throw
>>>>at the neighbours cats.
>>>
>>>Aaaack.  ;-(
>> 
>> 
>> I believe I measured a whopping 12ohm resistance between Vdd and Vss.
>> 
>> Paranoia now has me keeping my finger on top of the uC the whole time
>> it's on feeling for a temperature difference.
> 
> Been there--even slightly burned my finger!  ;-)

I've fried too many chips outside the kitchen for my liking. Speaking of
which I actually did the silly thing of trying my teeth on the uC after it
burnt out. I did this to confirm my suspicion that I had destroyed a
ceramic packaged one.

Did you burn your finger on the ROM or something different?

> 
>>>Just the other day, I found an Apple ][+ ROM (the E8 ROM) that is
>>>a near short from +5v to ground--it also makes a nice heating element!
>>>
>>>This is the first time I've found a ROM with this failure mode.
>> 
>> 
>> Was the extent of the failure isolated to the ROM? I'm surprised too that
>> it died. Electronics don't come much more robust than a ROM.
> 
> I was amazed.  That was the only failure, though it may have induced
> the power supply to fail (it doesn't work).

Yeah, that was probably it. My powersupply was taken out by a cap with a
snapped lead shorting out something on my Z80 soft card. Whatever it
shorted out it cooked the transistor near the Z80. I still need to replace
this to see if it can be made to work again.

Now I have the slightly more robust PC supply. Only slightly though. There
are some things the pictures don't show that I'm truly ashamed of.

> 
> 
>> Glad you think so. Do you think that using a soft encoding method like I
>> attempted is wrong? I have my doubts about it. It's just it was easy to
>> modify my board to try it so I did.
>> 
>> To do it I disconnected my erroneous connection of the write signal from
>> the hex inverter and connected it to the uC. I also connected a pin of
>> the uC to the write enable pin so I could get feedback on when it wants
>> to write.
> 
> How fast can the controller poll the input and produce an output?
> The write signal should be on time within a fraction of a microsecond.

Hmm, lets see. The uC is running at 12MHz. It can complete pretty much any
instruction in 4 clock pulses. I think things like branches may be 6 or 8
though. I don't remember. So best case of pure polling we have it hammering
around in a single instruction loop. This would be because all memory in
the PIC micros are registers, and IIRC all can be used directly in opcodes.
Ie memory-memory architecture, but because there are no bus overheads
because it's just a register file, and Harvard architecture so data and
code access are done concurrently on separate busses... What was I saying?
Best case it could realistically do it maybe 2 million times a second. I
don't think there is any overhead for reading IO bytes. There is for analog
pins though.

My only concern is with the small delay introduced wiping out some data
afterwards.

Tristan.
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