1 Dec
2011
1 Dec
'11
3:47 p.m.
On Dec 1, 2011, at 5:58 PM, Eric Smith wrote:
I would second this description wholeheartedly. What the DiscFerret and similar devices
are doing is *re-quantizing* the data which has been *de-quantized* (i.e. randomly
perturbed) by the drive mechanism and other random factors (including things like the
differences between the controller that wrote the drive with arbitrary base frequency and
drift). After the signal has been re-quantized, it often needs significant work on it to
re-align it in the time domain with the expected clock (thus the separator).
- Dave
(Perhaps we
have different concepts of what 'time-quantised' or
simply 'quantised' means. While there are differences, one might
ask the same question of an async serial signal for a simpler case to examine.)
It appears that you've identified the reason we disagree.
I would argue that asynchronous (start/stop) serial as received is non-time-quantized,
although the clock recovery is much simpler than with a magnetic disk because the channel
does not distort the timing by more than a trivial amount in proportion to the transmit
rate. A UART does have to oversample the async receive data and use a decision process
(generally based on detection of the leading edge of the start bit) to identify the
appropriate bit cell boundaries to time-quantize the data.
A synchronous serial channel provided with an explicit clock signal is time quantized.