[simpits-tech] MCC838 - Obscure decade counter chip

[alex]

>  -------Original Message-------
>  From: Alan Murray <realclassclown at yahoo.com>

>  A proper truth table in the Motorola documentation
>  would really help.

You're not kidding.

>  Specifically the Q4(not) ties back
>  to the second gate input. When your reset drives that
>  high, the 2nd gate (essentially a NOR) correctly
>  drives Q2 and subsequently Q3 low which gives you the
>  output you are getting...

>  What does the counter do without the NAND gate in the
>  circuit? Same thing right? 

Actually, no. If the Cd line is left High (No NAND gate), then Q4-Q1 counts 0000, 0001, 0010... 1000, 1001 (0-9). And in 2 places where I need the full decade counter this configuration is currently working as I need.

Somewhere I found a snipit of text (buried in a patent application I believe), that claims that if SD4-SD1 are high, then driving CD High to Low should reset the counter. If CD is Low, then driving any of SD4-SD1 High to Low will cause the corresponding Q4-Q1 to go High. But without the proper truth table even better verbage from Motorola, this little critter is turning out to be quite the little black box.

Alex