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

[RETRO Innovations]

     On April 22, 2019 at 8:04 PM Joel Rees <[1]joel.rees at gmail.com>
     wrote:
     2019´423¥(«) 4:55 James Ross <[2]jrosslist at outlook.com>:

     Ed Snider wrote:

     It's always best to refer to the datasheet for a particular device
     if

     possible
     I am trying to learn how to do that! :)
     I am going to go back and re-read some (some rather lengthy)
     articles on
     pull-ups and pull-downs and try to understand the underlying reason
     they
     are needed and the formula and numbers they are plugging in.

     Back when I read datasheets regularly, the manufacturer's datasheets
     usually gave a nod to best practices for the device, based on the
     internal
     design and the features the manufacturer was claiming.
     If the manufacturers no longer tell things like this, we as an
     industry are
     in serious danger. I hope 2nd source suppliers will at least refer
     you to
     the specs from the original manufacturer.
     I gather so far it has to do w/ limiting the current. Using just
     enough

     that is needed for a stable circuit w/o using too much.

     For inputs, right. There will be some dependency on the surrounding
     circuitry, on things like frequency, impedance, operating voltage,
     and what
     kind of current is being drawn on the outputs, but, again, the
     specsheet
     should make some indication on that.

   Specifications do continue to provide taht data, but it requires a bit
   more work.  It noted I (in), and V(hi) and V(lo) for inputs, but the
   calculation to decide on a resistor that will provide the minimum input
   current is left as an exercise for the reader.

   But, with CMOS families today, the rquired input current on anything
   you will find in the extended IC catalog will require like than .5mA,
   so 10K is really overkill (but is almost always fine).

   Jim

References

   1. mailto:joel.rees at gmail.com
   2. mailto:jrosslist at outlook.com