From: Jim Brain (brain_at_jbrain.com)
Date: 2004-10-21 17:41:40
> The same holds for RS232 (asynchronous operation): Every byte is sent
> asynchronously, thus, you cannot know beforehand when a byte will be
> sent. Anyway, as soon as it starts, the bits are just sent
> synchronously. You need a synchronous system to catch every sent bit,
Definition of synchronous: "Synchronous communication is sending data with
synchronization to an external clock" (wordiq.com)
Thus, we'll agree to disagree here. The entire RS232 sequence is asynch,
as no external clock is in play. SPI (available on many uControllers) is
synchronous, because it has an external clock line. IEC is both, having an
asynch part (the preamble/postamble) and a synchronous part (the data
transfer). Clock=Synchronous. No Clock=Asynchronous. It goes without
saying that synchronous operation is almost always easier to handle,
because the events can be gated with the clock, where asynchronous
requires stable internal clocks for timing purposes.
However, this is not the word enrichment list, so I'll move onto other
topics.
All command bytes in JDos are sent the normal way, with the drive doing a
bit twiddle on the data line between bits 7 and 8 (counting from 1), You
might be able to watch for the last command byte, and then know the data
bytes are coming/going. I think, though, the 64 initiates all transfers
(it signals when it will send data, it signals when it can accept data),
given the issue of the badlines inherent in the 64.
Jim
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