Re: Plus/4 RS232 woes

Den Thu, 6 Sep 2018 19:56:26 +0200 skrev Gerrit Heitsch
<gerrit@laosinh.s.bawue.de>:
> On 09/06/2018 07:40 PM, Nils Eilers wrote:
> > On Wed, 5 Sep 2018 16:39:44 +0200
> > Gerrit Heitsch <gerrit@laosinh.s.bawue.de> wrote:
> > 
> >> The 6551 doesn't need capacitors or resistors. All you need is to
> >> connect the crystal to the two XTAL pins and you're done.
> > 
> > The W65C51N datasheet shows a schematic at page 19 with a 30 pF
> > capacitor from XTALI to GND and a 1 M-Ohm-resistor from XTALI to
> > XTALO.
> 
> Well, that's the 65C51... I was talking about the 6551 and its
> datasheet doesn't mention anything of the sort.
> 
> And if you look at the schematics of the Plus/4, you'll see that
> there is only the crystal.

Not deriving the baud rate clock from the system clock must have added
to the cost.

Of course you'd need a divisor that isn't as nice as 16 to get correct
baud rates with a clock that can also be used to generate a NTSC or PAL
color signal. If the 6551 addition had been in the plans when TED and
CPU were designed for the Plus/4 series, they might have had that
buildt in.

Btw a "6552" which can take color clock might had been something they
could sell anyways.

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