Joined: Fri Aug 30, 2002 1:09 am
Posts: 8546
Location: Southern California
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BigDumbDinosaur wrote: What is the purpose of the CD4082? 4000-series logic is very slow, even at elevated voltages. It's a dual 4-input AND gate. It wasn't in my NSC books, so I had to look it up online. Its max prop delay at 5V is 250ns! It should be ok of the IRQ\ ANDing, but Justin, for the EEPROM address decoding, if you ever go beyond 1MHz, you'll want to use at least 74HC logic. I know it will require two gates to replace the one, but the combined propagation will still be much, much faster.Quote: Also, it would be more informative if gates are drawn as gates, not boxes with pins. An AND gate drawn as an AND gate is much more informative than a collection of six AND gates in a rectangle. Try as I might, I just can't remember all the part numbers and what they do. Justin, it will always be good to draw out the actual gates, rather than drawing rectangles with, in this case, A, B, C, D,... down the sides. I expanded the "General Steps For A Successful Project" page of the 6502 primer to add a section (actually now the entire last half of the page) on "Getting help on the 6502.org forum."Dr Jefyll wrote: To speed things up I've reproduced your drawing in the style I (and many people) prefer. Thanks. I wasn't able to read the dark blue labels against the black background without getting up off my chair and getting really close to the monitor. It looked like there might be something there, but that was the extent of it, even though my vision is very clear.
Why are there two clock circuits with their outputs tied together? Are they just options to plug in two different sizes of packages, and only one will be there at a time? (Otherwise you definitely don't want two outputs fighting each other.)
On sheet 4, I strongly recommend putting at least a ground connection on the PORTA and PORTB connectors, if not also the +5V. Further, you could use dual-row pin headers (so you can plug standard-sized IDCs into them) and put ground pins on opposite corners, and Vcc pins on the remaining two opposite corners, so if something gets plugged in backwards, the power and ground will still be correct and you won't destroy anything. Standard IDC (insulation-displacement connectors, which you press onto ribbon cables) come in 10, 14, 16, 20, 26, 34, 40, and 50 connections.
Be sure to add debouncing to your reset circuit. The potential problem and remedy is described in the reset page of the 6502 primer. Be sure to go through the entire 6502 primer though. It was initially written about 20 years ago to address problems and questions that kept coming up on the forum, then I finally got my own site and got it posted in 2012, and I keep making improvements to it regularly. It's in 22 logically organized sections. It will save you a lot of grief.
I'd like to see comments about the USB keyboard circuit from anyone who has looked into USB more than I. I have a fat book about it, but have not looked in depth at the timing._________________ http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?
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