[Coco] What do you use for pull-up and pull-down TTL resistor values? (LS series) (coco related project but possibly OT)

[James Ross]

Joel Rees wrote:
> ... datasheets
> usually gave a nod to best practices for the device ... 

Good advice ... however, they can get really technical very quickly and just assume that the reader is up to speed on all the jargon. I want to learn the jargon eventually, but first I want to understand the "basics" -- input and output voltages & current maximums / minimums.  Even just those at my level are a bit challenging to identify and understand fully.    

> ... CMOS ... /... TTL ... /... others ... 

Yes, I am slowly catching on to the various families of chip technologies and one must know what they are doing to mix them.  I also understand that TTL / LS series is the old school tech from back in the CoCo days. And that tech is deprecated and anything new should be using the HC series (or better?). But I want to wrap my head around the old-school retro stuff first. 

> Rules of thumb work pretty well at MHz clock rates.

That is good to know! And precisely what I am trying learn here at the beginning (I've been at it for quite a few months already … years if you count the "off" periods ...). 

> ... at some point
> you'll want an oscilloscope to see what the real results are. 

Ah yes, I need to get one eventually and learn to use it.  

> Circuit board trace
> shape and length aren't usually critical at MHz rates, but do become
> problematic somewhere around 100 MHz, etc.

If I ever get into the 100 MHz range or greater, I'll be like wow -- I can't believe it! :) 

Right now I am looking at 1 to 2 MHz possibly up to 4 MHz playing w/ 6803 and 6x09 processors. 

At some point going higher up to 25 MHz w/ FPGA's driving stuff …

I did actually buy a couple of Z80's (along w/ the Motorola CPUs) that can be clocked at 20 MHz which I want to play with (Oh no, heresy, not zed 80's!)!  IF I keep at it, eventually, I want to play w/ the MC68000 series starting w/ the 68008 – we’ll see how far my motivation and interest in electronics lasts.  Hopefully from here on out. 

I am really doing this so I can create that ultimate Real Time Clock! (RTC) ... (Insert evil laugh, here!) :) 

James