C204 & the PLA

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frotzen
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C204 & the PLA

Post by frotzen » Mon Aug 07, 2017 1:32 am

Hello,

I am testing a few PLAs on "black screen" boards just for the experience. I have the PLAnkton, which I favor, and the PLAtinum. I use the PLAnkton in my personal C64 since I don't need to add C204 to the board (250407). My question is in reference to the other one, and specifically C204 which is shipped with it.

I've noticed in the schematics for artwork 251138, C204 is between pin 15 of the RAMs (U9-U12 & U21-U24) and Ground. The instructions for the PLAtinum specify soldering C204 between pin 15 of the RAMs and +5V pin 8 of the RAMs. Does it matter? I prefer to install C204 between pin 15 and Ground since it's easier (between R42 !CAS side and C41 Ground side). I can't think of a reason to prefer +5V over Ground, other than current flow theory (+ hole flow vs - electron flow).

Thank you,

frotzen



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eslapion
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Re: C204 & the PLA

Post by eslapion » Mon Aug 07, 2017 5:00 am

frotzen wrote:
Mon Aug 07, 2017 1:32 am
... I've noticed in the schematics for artwork 251138, C204 is between pin 15 of the RAMs (U9-U12 & U21-U24) and Ground. The instructions for the PLAtinum specify soldering C204 between pin 15 of the RAMs and +5V pin 8 of the RAMs. Does it matter? I prefer to install C204 between pin 15 and Ground since it's easier (between R42 !CAS side and C41 Ground side). I can't think of a reason to prefer +5V over Ground, other than current flow theory (+ hole flow vs - electron flow).
I suspect this may also have something to do with the fact C204 is a component that's part of an RC filter to delay activation of the _CAS signal of all 8 DRAM chips. Since _CAS is active low and a capacitor has zero voltage drop at power up, it's better to make sure _CAS is pulled up when the computer is starting up.
Wealth, like happiness, is never attained directly. It comes as a by-product of providing a useful service. -Harland D. Sanders

frotzen
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Re: C204 & the PLA

Post by frotzen » Mon Aug 07, 2017 6:32 pm

Ah. Yes, I see that it would start in an inactive state with C204 across pin 15 and 8. I didn't consider the starting state since _CAS is a "not", just the RC filter delay was necessary.

Thanks,
Frotzen

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