gfoot wrote:
Additionally, the first counter's ENP is connected to the second counter's ENT. I'm not sure why they do this, as trying to enable/disable counting for the whole chain by changing the state of this input would lead to another ripple effect. It feels like you should just connect this high all the time, and use the first counter's ENT instead to enable/disable the whole array, which will again have a constant response time regardless of how many counters are chained.
That was a incredibly detailed response. Thank you for that. I will actually be reading that at least 2 more times before I'm satisfied.
In the meantime, I don't have these chips on me at the moment, and oscilloscopes are not my strong suit. I have the datasheet, and I have your feelings on this. You told me you were using some of these '163 chips, but did you not cascade them for any reason?
I exactly agree with you by the way! I'm looking back and forth on Figure 1 and Figure 2, and I'm not seeing a big difference in the end. I was planning on always setting Chip #1 ENP and ENT high, thus Chip #2 ENT also high. Chip #2+ ENP is set to Chip #1 RCO. And then I daisy-chain the Chip #n RCO to Chip #n+1 ENT. This is the configuration on Figure 2.
Funny side note, Ben Eater uses Figure 1 on his schematics:
https://eater.net/vgaThough, he is using only 10 MHz, while here I'm forced into a 25.175 MHz oscillator (unless you can find me a 12.5875 MHz oscillator somewhere!).
Lastly, going from Horizontal Counters to Vertical Counters. Ben Eater uses the 'horizontal reset' logic as the actual clock pulse for the vertical counters. That has always been in my mind as the way to do it, even now with these 4-bit counters. There will be ripple at some point I guess. Perhaps I'm just trying to minimize it.
Thank you George, I'll be reading this over again, and again!
Chad
EDIT:
I re-read it all over again. Its making more sense the second time around, though I'm still a tiny bit puzzled why Figure 2 is somehow better than Figure 1. I will read it one more time (at least), but it makes much more sense now. Thank you again.
While I'm editing, I have made these Figure 2 changes to my printed board, and it's nearly done. I plan on re-constructing my 6502 board so that it can plug directly into this board, so that might take a bit of time. I'm likewise going to solder my existing 6502 printed board to make sure that what I have made will work as assumed. Wouldn't want to go printing another board if I haven't even tested the first one! Time time time.
Thanks!