Home network - big question!

[rod at tpgi.com.au]

Sam Couter <sam at topic.com.au> wrote:-

Just to clear up a few common misconceptions.

>[ Disclaimer: I'm no expert. I believe what follows to be the truth, it's
> what I've learned and been taught over the years, but it may still be
> wrong. ]
> 
> The 8250 UART can only operate at up to 19200 bps, good for a modem up to
> 9600 baud.
>
Thankfully you couldnt get one of these in a product today if you 
tried - they are 186/286 era IC. Found on really old ISA cards.

> The 16450 can only operate at up to 57600 bps, good for modems up to
> 14.4K.
> 

The 16450 can handle 115.2K no problems. However due to its lack 
of a FIFO (only 2 bytes of buffer) it will generate lots of ints at this 
rate (one per character).  Fine for Linux on a 486 or better but a 
problem for Windows (move the mouse - lose a packet :-). 
Once again you would have trouble finding one of these new now. 
However they were common on early cheap all in one MB's for 
Pentiums and posibly 486's IIRC. Common on printer/games/serial 
ISA cards.

> The 16550 is BROKEN. Don't buy a computer with one.
> 
The Nat semi 16550 is broken and no longer exists - immediately 
replaced by the Nat semi 16550a. Clone 16550 are actually bug free 
IIRC. Thankfully no motherboard is fitted with these lame ducks, now 
only found on some old ISA cards.
 
> Tha 16500A is what the 16550 was supposed to be. It operates at up to
> 115200 bps and suits modems up to 57K.
>
16550A. 
 
> Anything slower than a 16550A will be a detriment to bandwidth over a
> modem, unless your modem is slow anyway.
No - but as above it will pose an interupt load problem on OS's with 
poor int response times IE any Windows.


Basically if its just a modem connection with linux and the hardware 
is 486 or better chances are the UART choice is not going to effect 
the application. 

If you are really concerned about interupt loads there are 
16650,16750 and 16850's out there which have relatively huge 
FIFO's.

Hope this helps 
-RodT