[Coco] CoCo1 Rev E 64K Upgrade by Kitsz

[Gene Heskett]

On Sunday 14 September 2008, Joel Ewy wrote:
>Darren A wrote:
>> ...I've seen two other
>> documents say that a 33 ohm resistor needs to be soldered to those
>> pins. My board has a jumper between those two pins rather than a
>> resistor. Does anyone know if that could cause a problem?
>
>Jumper = low ohm resistor...  :)

It is also a ringing damper, using the conductors capacitance and the resistor 
as an rc filter.  It helped to keep the coco quasi-legal with the fcc's early 
rules for radiated noise.  33 ohms has minimal effect on the circuitry, but 
when the FCC got pickier and they had to use 120 ohm r's to make the grade, 
this started getting into the logic zero pulldown, which in turn reduced the 
noise margin of the circuitry, sometimes enough that many of those machines 
have had them shorted out for 20 years in order to run with stability.

>> Darren
>> ...
>
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-- 
Cheers, Gene
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