8251 troubles - test-drb@ccmp.vtda.org

28 Apr 2008

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Subject: RE: 8251 troubles
   From: "Chuck Guzis" <cclist at sydex.com>
   Date: Mon, 28 Apr 2008 11:22:58 -0700
     To: cctalk at classiccmp.org

  Date: Sun, 27 Apr 2008 15:41:49 -0400
 From: Allison   
  I have both in quantity.  Generally it's the
quirks of the 
 "improved part"that are annoying but for simple Async serial IO
 they are identical enough. 
It could be that simple polled-mode async I/O works well enough, but 
when I was trying to get a bisync package working with the 8251, I 
wanted to chew my own arm off.  Among the issues (other than the 
occasional device "hang") that I had was the lack of double-buffering 
and the indeterminate control logic (it was possible to disable the 
transmitter in the middle of a character).  The 8251A was *much* 
better in that respect.

For async its ok bisync, you gotta be crazy.  While the A helped 
bisync it broke the CTS/ CTS to inactive during a TX meant the 
character would be resent!  The Fix was for both A and non A
is a gate to interlock the external CTS/ with TXE.

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 In any case, Dwight has the NEC part which renders the
topic moot. 
Not really as it had the exact same bugs.

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I found at the time that the Signetics 2651 was a far better chip for 
most utility purposes than the 8251, having the benefit of an 
internal baud-rate generator for async operation.  
It was better.

Allison

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 Cheers,
Chuck 