Modulo12 UP/DOWN counter needed

[stragenmitsuko]

I'm trying to design a 12 counter/divider .
Not that hard at first sight . There are plenty
synchronous 4 bit counters with presets and asynchronous reset .
Simply decode D, E and F hex , and have the decoding logic reset the counter to 0000 et voila .

This will work perfectly when counting up , but when counting down
it will go from O to F hex , reset to 0 , step down to F hex , decode and reset etc etc etc .
When counting down it ought to go from 0 to C hex .

So , before I start digging up my old scool books , maybe someone has a
working circuit available .

Brief , I need a 12 counter ( 0 to C hex ) wich can count both up and down from any position . Synchronous , reliabe and free of transients and spikes .
It'll be used to contruct a 3phase bipolar stepper driver .

Pat

[Eurisko]

Have the decoding circuit generate a preload (not reset) when D, E , or F is output.


Preload bits 0 and 1 are tied to ground.
Preload bits 2 and 3 are tied to the inverted direction line (up=1 down=0)

This will preload the count to 0 or 12 depending on whether you're counting up or down.