[time-nuts] low power divide by 5

[Gerhard Hoffmann]

Am 02.07.20 um 00:35 schrieb jimlux:
> On 7/1/20 1:41 PM, ed breya wrote:
>
>> Yeah, I know. I was just lamenting the lack of nice medium-density 
>> count functions in 74AC. It's hard to beat the simplicity of a '390 
>> when you 
>
16 bore holes just to deploy 4 flip flops is not what I'd call 
simplicity. And Fairchild
recognized that as well. The 390 did not make it into the 1987 Fairchild 
Advanced CMOS
(FACT) data book.
They expected other chips to sell better, like the 74ACT488 GPIB / HPIB 
/ IEEE488 bus
interface. Ever used one? The market for Nixie clocks with one counter + 
one decoder
per digit must have been smaller, even back then.

>>
>> Anyway, I've always liked having a wide assortment of MSI logic 
>> devices available in all families, that you just hook up and it goes 
>> - no setup, no programming. I've saved lots of counter types for 
>> possible use. One obscure one is the MC14566, with divide 6 counters 
>> for clock time readout and generation, in the old days.
>
> That's sort of the design goal for the 22V10 and earlier PAL devices - 
> keep them in familiar DIP packages, power on the corners like the IC 
> gods intended, and you can program it to replicate a whole variety of 
> MSI functionality, often with the same pinout.
>
>
Corner pinning for Vcc and GND is not what any gods intended. In FACT, 
(pun intended)
it's evil. Remember ground bounce? The corners are the worst locations 
on a DIL chip
you can find for that job. And fig leaf capacitors across the chip are 
just that.
At 100 MHz, they simply are not there. The optical illusion helps only 
to hide that.
The 3  ACT chips on the experiment board posted yesterday reminded me of 
the
last pages of this:

< 
http://www.hoffmann-hochfrequenz.de/downloads/experiments_with_decoupling_capacitors.pdf 
 >

The golden times of logic design are now, not then!

Gerhard