Re: USB to RS232 one chip solution

"mkr5000" <mikerbgr@xxxxxxxxx> wrote in message
news:0aceff00-aba2-47f6-9a1e-3d10923f90a0@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
The downside of USB I suppose is the complexity of it's approach and
hence, the inability of Windows to integrate with it in a plug and
play fashion?

Well... the better perspective is that ALL hardware needs a device driver as
such in a modern operating system, the question is just whether the OS
manufacturer (e.g., Microsoft) already *included* that driver when the OS was
installed or if the end user needs to provide it themselves.

It seems to me I've had some devices that were plug and play without
drivers (if I remember right) and some where there were drivers that
needed to be installed.

Yes, Windows comes with literally thousands of drivers included, but that's
nothing compared to the many tens or even hundreds of thousands of different
bits of hardware out there.

I wish I knew more about why that is.....must be some very specific
information required in code, I guess.

Compared to a "regular" RS-232 serial part, USB is many times more complex --
on the order of, e.g., a PCI bus. But, there's something else going here that
many people don't realize: With RS-232, someone has to sit down and define a
protocol for the device in question (unless it's just, e.g., a terminal
program!), and implementing that protocol ends up in an "application." In a
sense, then, the protocol handling code *is* a "driver," it's just installed
by "setup.exe" rather than the plug-and-play manager. With USB, while there's
often still some amount of protocol that needs to be defined for custom
devices too, it's nowhere near as much as with RS-232 -- at least if the
RS-232 device needed comparable robustness: The Windows USB drivers take care
of loading the right driver based on the device attached, it takes care of
buffering USB packets and sending re-tries upon errors, and takes care of
scheduling for time-critical (isochronous) transfers. Hence, RS-232 vs. USB
isn't really that different in that both need drivers, it's just that the
division of *where* the driver ends up (as a Kernel-mode device driver or a
user-mode application) has been set up so as to try to keep some of the
complexity of USB from having to be dealt with in user-mode code.

---Joel


.

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