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jbaum81
PostPosted: Tue Nov 16, 2021 8:15 pm 
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Posts: 25
Hi guys,

Upgraded my initial 6502 board design and I have left over 4 untouched PCB's compatible with the Commander X16 addressing using some Atmel PAL's for address decoding and soft power circuit using an ATTINY. The board works great, but does require a single bodge as I failed to connect the pullup to the reset line. I can also include an expansion card that introduces dual UART via the SC28L92 chip and an RTC.

All I ask is that you pay shipping, I can share the original Kicad files and answer any questions.

PM me if interested.


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BigDumbDinosaur
PostPosted: Tue Nov 16, 2021 10:48 pm 
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In looking at your unit I happened to notice that the I/O header has no grounds. Was that an oversight? I foresee AC performance problems without them.

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jbaum81
PostPosted: Wed Nov 17, 2021 3:50 am 
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BigDumbDinosaur wrote:
In looking at your unit I happened to notice that the I/O header has no grounds. Was that an oversight? I foresee AC performance problems without them.


grounds are on the right. The expansion card sits on top of all 3 headers. Below is a 3d rendering of the serial io card I have on it.


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GARTHWILSON
PostPosted: Wed Nov 17, 2021 5:09 am 
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In the future you'll want to get the ground connections closer to the signal connections. At the applicable frequencies (resulting from rise/fall times, not clock frequency), the energy flows not in the copper but rather in the space between the signal line and its return; so if that space is large (because the closest ground connection is far away), there will be a lot of inductance, causing problems. Here's one video that addresses this:
https://www.youtube.com/watch?v=ySuUZEjARPY
It's long, and it mostly deals with PCB design; so if you want something short, start at 12:20 and just go four minutes. I know I've seen a better one for explaining this in your situation. If can can remember where it was, I'll come back and edit this and put the link here. If you had two ground pins (or a ground and a bypassed power) in a long connector, it's best to distribute them so as to minimize the greatest distance from any signal line to its ground return.

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tokafondo
PostPosted: Tue Nov 30, 2021 9:31 pm 
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GARTHWILSON wrote:
Here's one video that addresses this: https://www.youtube.com/watch?v=ySuUZEjARPY


So many things to learn...
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