4 Dec
2011
4 Dec
'11
1:15 p.m.
On 2011 Dec 3, at 2:03 PM, Tony Duell wrote:
Well, I wasn't really thinking of the controller, rather the signal
one typically sees, which - if you like - implies a controller, as
something wrote the original signal.
The original context of the thread was recovering digital data from
an ST-506 drive, albeit one with unknown controller characteristics,
"Waveforms" were mentioned. I allowed for the benefit of using an
analog-in-the-time-domain assessment of the signal from the drive in
my first message.
(And here I thought we would have agreed, based on your assessment of
the async serial signal vs. cat notifier).
Why would I argue as you suggest? It is a question which does not
follow from my statement. Your question which I was answering
referred to the "receive data output" of the modem.
If there is a debate still it seems to be one of semantics. Is a wire
interconnecting a gate output and gate input of two TTL ICs in a
synchronous system analog? Or is it an analog *link*? Or is it just
*capable* - if extracted for another use - of being an analog link?
Or does it just have some analog characteristics? Or does it merely
have the capability of *conveying* analog information when used in an
other context? One could answer yes to all those, depending on the
nuance one wishes to put on it. While it can be useful and necessary
to analyse the signal on that wire in analog terms at times
(prototyping, repairing), do we normally think of it or treat it as
analog? I didn't think so: because we know something about the
characteristics of the signal we expect to see on it.
In my response
however, I was distinguishing between the assessment
of the signal and the properties of the signal, as your response had
alluded to the latter, although we also have the two perspectives to
consider of the agglomeration of possible signals from all disks
versus a given instance. Leaving aside the low probability or
occurrence of someone using the disk for analog PWM or PPM recording,
and other opinions notwithstanding (other thread), I do not consider
a given instance of a (typical) amplitude-normalised (to two states)
read signal from the disk to be analog in the time domain, but from
your other message I think we agree on that.
I think the difference between our approachies is that you're
consisderign a drive and a particular controller combination, I am
considering jus tthe drive. I agree that the data sent from any normal controller
to th edrive
when
writing (or formatting) is time-quantized. And that the data read back
from the drive is similar, modulo a bit of jitter and the magnetic
effects that perecompensation is designed to compensate for.
However, sicen ST506 is a low-level 'raw' interface, you can't
assume the
time quatization is the same for all possible controllers. Sicne the
pulse spacing could be any vlaue between given limits (although a
particlar contoller will only use a few differnet psacings), I feel
the
drive itslef is analogue in the time domain.
In the analogy
with the FSK modem in your other message then: simply
put, whether the demodulated signal is time-quantised depends on the
properties of the modulating signal.
Are you going to argue that a piece of wire is a quantized
communications
link just becuase you can send regualrly spaced pulses down it?