[Coco] 16550 wasRe: RS232 paks

[Mike Pepe]

Roger,

The 6551 does have a nasty bug where a state change in the hardware flow
control causes partially transmitted (or assembled?) characters to be
dropped.

I would guess that in what you're doing, things are totally software
driven and in tight loops where such conditions would not happen.

In a multitasking environment such as OS9 what Mark says is much more
applicable. I'd agree in that situation I'd take a 16550 over a 6551 any
day. 



-----Original Message-----
From: coco-bounces at maltedmedia.com [mailto:coco-bounces at maltedmedia.com]
On Behalf Of Roger Taylor
Sent: Wednesday, March 04, 2009 11:40 AM
To: CoCoList for Color Computer Enthusiasts
Subject: Re: [Coco] 16550 wasRe: RS232 paks

At 09:40 AM 3/4/2009, you wrote:
>Willard,
>
>The NitrOS-9/Driver is already written for a 16550 device. I have 
>had a homebrew card running for almost 10yrs based upon that chipset.
>
>Yes, it would break all the old term programs. A caveat of adding 
>new technology to an old machine. Not a problem in NitrOS-9 as the 
>driver/dd is not part of the actual program, when properly written.
>
>The SuperBoard has a multi-function chip on it that has the 16550 in 
>it. Anyone that has done high speed serial testing in a system will 
>design it with hardware handshaking. It is no secret that the 
>ACIA(6551) has issues with this, plus almost no buffer space. Not a 
>good choice for new designs, IMHO. 16xxx series offers GREAT 
>buffers, programmable interrupt thresholds etc..... I guess that is 
>why they are so common, oh they work too! :)
>
>Regards,
>
>Mark
>Cloud-9


Mark,

Exactly what problems have you yourself had with the 6551 so that I 
may try to offer a software solution?  I'm not claiming to have all 
the answers, but I've done a serious amount of 6551 coding in the 
past, and I can assure you that the chip itself is not always the 
problem.  The programmer is 90% of the problem.  The OS is 90% of the 
problem.  If there's some little bug or dislike about a certain chip, 
I guarantee that there's the same number or more in the 16550.  I've 
read about that chip and based on how many variants are floating 
around, how can anyone ever agree on a right way to code the 
routines?  It appears to be a mess, no less than what you claim about 
the 6551.  I'm not saying any certain chip is BETTER than the other.. 
I'm saying that TOO many programmers and nonprogrammers have clashed 
about these chips and in the end, they're all still being used 
today.  You can always tell when the programmer took shortcuts or 
just didn't know what he was doing.

When you say the 6551 is not a wise choice for any new designs, your 
intent is clear but the statement is not true.  Someone who's put out 
a new wireless RS-232 pak didn't just wake up yesterday and discover 
the 6551.  People who know how to write good software aren't afraid 
of the 6551.

My wireless RS-232 pak has been connected to 7 CoCo units (2 CoCo 
1's, 1 CoCo 3, 4 CoCo 2's) and to 2 PCs @ 115200 bps running lengthy 
looping tests (1-2 days sometimes), and I haven't seen it bomb out 
yet.  Can you please tell me what circumstances I need in order to 
break my protocol ?






-- 
Roger Taylor

http://www.wordofthedayonline.com


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