Tony Duell <ard_at_p850ug1.demon.co.uk>
> I don't think many CD players have a microprocessor in the audio decoding
> section. In other words the error correction, etc is done by dedicated
> logic.
Of course. Even today, few microcontrollers would be fast enough to do
the decode and error detection/correction in real time. It wouldn't be
cost-effective to implement that way. Dedicated logic in a gate array
or custom chip is easier, and it only takes a few thousand gates. In a
design optimized for tubes, the number of gates could be reduced
substantially, but for gate array implementation there was no motivation
to work hard at reducing the gate count.
> But even the early players had, perhaps, 2K RAM in the decoder
> section that would be a pain to do with valves.
That's the de-interleave memory. It would be implemented with core memory.
> Microprocessors are normally used in the user interface and servo control
> sections of CD players (although the servos themselves can be entirely
> analogue and only use the microprocessor for track skips, etc).
The early CD players used analog servos; the newer ones use a simple DSP
embedded in the decoder chipset. I've never seen a CD player that used a
general-purpose microcontroller as part of the servo system, though I suppose
it is possible.
> But it would be possible to not use them there without too much work.
My point was that the CD format (and specifically, the "P" subcode) was
deliberately designed not just so that a microprocessorless CD player could
be built, but that it actually would be easy, and that it still could have
track forward skip and track reverse skip buttons.
Of course, by the time CD players were commercially manufactured, it was
more cost-effective to simply use a mask-programmed four-bit microcontroller.
Cheers,
Eric
Received on Mon Feb 01 1999 - 17:19:40 GMT