2 May
2012
2 May
'12
1:54 p.m.
On May 2, 2012, at 2:57 PM, Tony Duell wrote:
Didn't say it wasn't. :-) I was just commenting on why they might have
made it asymmetric. I'm clearly not a fan of that fact, even if it does
slightly simplify the hardware.
I doubt that
was why they did it, though. I'm sure it had much more
to do with simplifying device electronics so they could be implemented
on very cheap microcontrollers at low power consumption, rather than
Actually, thats' 2 more resons in favour of RS232 for me... Secondly, the fact that RS32 does not use TTL (or 3.3V
logic) levels
means that most microcontrolelrs/FPGAs/etc (if not all) could not drive
it direcrlly. For a proper implementation of an RS232 interface you had
to have some sort of buffer, like a MAX232 chip. And that would bear the
brunt of any zaps on the interfce connector [1]. Such a chip is a lot easier
to get and replace than a programmed microcontrolker for a device that
you've never seen before.
A lot of microcontrollers require external PHYs for the higher-speed
stuff, just because the signal is analog-ish and it makes it a little
easier to avoid heavy mixed-signal design. Same reason you never saw
many microcontrollers without RS-232 level shifters on them (aside from
the fact that you wouldn't want to tie the customer down, as they might
want 422 or 485 instead, etc.)
I guess I don;'t want reliability... I'd
rather hace somethign that fails
mroe often when the parts that fail are easy to get and replace than
soemthign that fails evey 5 years where I have major problems getting the IC>
Well, it's a matter of modularity. I like compactness to a point,
especially if I'm trying to make something small. But if I want
reliability, I'll use separate USB and Ethernet PHYs.
[1] Although not always. The serial port in my HP9817
was defective when
I got the machine and I found that not only were the buffers damaged, so
was the 8250 serial chipe (yes, an 8250 in a 68K machine. Odd...). I am
not sure what had happened to the machine.
Odd indeed. Lots of 68K machines used 8350s, but that's a very
different chip.
- Dave