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From: jdeitch@umiami.ir.miami.edu (Jonathan Deitch)
Newsgroups: comp.sys.apple2
Subject: Re: //c serial ports.
Message-ID: <1991Mar26.191258.8367@umiami.ir.miami.edu>
Date: 27 Mar 91 00:12:58 GMT
References: <1991Mar26.043509.24160@sserve.cc.adfa.oz.au> <7175@munnari.oz.au>
Followup-To: comp.sys.apple2
Organization: Univ of Miami IR
Lines: 55

In article <7175@munnari.oz.au>, a.guillaume@trl.oz.au (andrew guillaume) writes:
> 
> In article <1991Mar26.043509.24160@sserve.cc.adfa.oz.au>,
> pgc@csadfa.cs.adfa.oz.au (Phil Clark) writes:
>> I seem to remember reading somewhere, possibly in this newsgroup, that
>> Applesoft basic has problems keeping up with data via the serial ports of
>> a //c at greater than about 1200 baud. 
> 
>> Has anyone else experienced this problem and if so, is there a simple
>> answer?
> 
>> The data format is 8 data bits, no parity, 2 stop bits, 4800 baud.
> 
> G'day !
> 
> I have had similar problems, at 1200 baud. Data format : 8 bits, no parity,
> 1 stop bit, 1200 baud. I was using Visiterm (a comms program), hooked up
> directly to my unix box, to download text. At 1200 baud, I would loose a
> character ot two every time the Apple //c would send a stop character to
> write to disk. No problems at 300 baud. I was wondering whether this was 
> a software problem or whether that was linked to the serial port. 
> Theoretically, the //c port can go up to 19.2k baud. So says the tech
> manual.
> 
> I would also appreciate if someone could shed light on this, and give
> an indication as to whether the problem disappears with an upgrade (I have
> to upgrade my //c from a "boat anchor" :-) to a unidisk in order to be able
> to buy a Chinook HD). Thanks in advance.
> 
> Andrew Guillaume
> 
> Internet : a.guillaume@trl.oz.au

On the "Boat Anchor" //c, Apple had some design problems with the serial ports.

It seems that they tried to derive the timing signal for the serial ports from
the 14.8 mhz master timing clock.  What they got was very close but not exact
to what the 6551 serial chips expect.  End result : garbled text and serial
communications problems.  This is fixed with later versions.

Here's how to tell which version you have : take your //c apart and see if
there is a silver TTL clock generator in the row of chips next to the power
supply.  If so, you shouldn't have any problems.  If not so (the third back is
a 74LS161) than you should be able to get a free motherboard upgrade from your
friendly Apple dealer.  BTW : they sometimes will give you the Unidisk 3.5"
motherboard as this upgrade for nothing extra.

Good Luck to all !

- Jonathan
 
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