8250 UART

8250 UART

Post by Lawrence Luci » Tue, 27 Jul 1999 04:00:00



Howdy all.....:-)

Firstly I do realize that there are newer/better UARTs available than the 8250
but a 8250 is all I have available right now to experiment with.  :-)

I need an URL to locate a schematic on how to hookup a 8250, 1488 and 1489.
I've spent the last couple of days searching the net but can't seem to turn up
anything except for one schematic that shows the UART but not the 1488 and 1489
connections.

BTW, this schematic shows the timing crystal directly connected (via R/C
components) to the 8250.  Is this correct?  Is there no oscillator (eg 555
timing) or binary counter IC (eg 74HC6040) needed for this UART?

Any information would be much appreciated..........thanks! :-)

--- Sqed/32 1.14/r15155

--- Squish->SOUP by TAM

 
 
 

8250 UART

Post by Bob » Tue, 27 Jul 1999 04:00:00



>BTW, this schematic shows the timing crystal directly connected (via R/C
>components) to the 8250.  Is this correct?  Is there no oscillator (eg 555
>timing) or binary counter IC (eg 74HC6040) needed for this UART?

You can probably use a crystal (can) oscillator to generate the clock for
this.  These connect to power (usually +5V) and ground and have a clock
output that goes to the UART's clock input.  You might be able to get by
with a 555 or some other RC circuit, but it probably won't be as clean and
consistent as a crystal circuit or a crystal oscillator.

Bob


www.saracon.com

 
 
 

8250 UART

Post by Stev » Tue, 27 Jul 1999 04:00:00




> >BTW, this schematic shows the timing crystal directly connected (via R/C
> >components) to the 8250.  Is this correct?  Is there no oscillator (eg 555
> >timing) or binary counter IC (eg 74HC6040) needed for this UART?

> You can probably use a crystal (can) oscillator to generate the clock for
> this.  These connect to power (usually +5V) and ground and have a clock
> output that goes to the UART's clock input.  You might be able to get by
> with a 555 or some other RC circuit, but it probably won't be as clean and
> consistent as a crystal circuit or a crystal oscillator.

> Bob


> www.saracon.com

------------------------------
You CAN use an oscillator on these UARTs, but it isn't necessary!!

The 8250/16450/16550/etc line of IBM-PC compatible UARTs ALL use a
crystal directly on their pins, and have an internal baudclock divider,
which can be used independent of the UART from its -BAUDOUT output pin,
which is then routed back into the UART in most designs. They often use
a 1.8432 MHz crystal which divides well into common baud rates. The
divisor is programmable internally.
-Steve
--

-Electronics Site!! 1000 Files/50 Dirs!! http://www.armory.com/~rstevew
Europe Naples Italy: http://ftp.unina.it/pub/electronics/ftp.armory.com

 
 
 

1. disconnect tied to 8250 uart???

I have a 486 with 32mb ram running win3.1        Just had a new
dedicated phone line installed.  Problem? I keep getting disconnected
while on the web -- rarely if ever in news -- and believe that my
problem may be the old 8250 uart.   Anyone have any thoughts or
experience on that?   I can pick up a new serial board with a 16550A
uart quite reasonably and looks very simple to install where the
old/current one is.  Do you think that will solve my problem?   The
only way I don't get disconnected is if I clear the cache while in
NN3.0 then exit, the restart.   If I don't do it frequently enough,
i.e. like every 6th screen I go to, I get kicked off..  Seems like a
lot of work to go thru.   Adding the 16mb of ram helped, but didn't
eliminate the problem.  Also, I have 620k free memory so I know that's
not the problem.    Any suggestions would be greatly appreciated.

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