Here's a web page with several JK flip-flop dividers, including divide by 5:
http://www.play-hookey.com/digital/counters/frequency_dividers.html Dave On 2020-06-30 15:47, dschuecker wrote: > Hi, > > a divide by five should possible with a synchronous state-machine made of 3 ( > sufficiently fast-) JK-FlipFlops. > > All 3 FFs are clocked with the input freq. , the outputs of the FFs are fed > back to the the JK-inputs, the divided freq. is output of one of the FFs. > > Additional constraints: no external ANDs or ORs or NOTs, the state-machine > does not get stuck in the 3 unused states. > > This turned out to be a very interesting problem and I do not yet come up > with a solution. Maybe there is none. Analytical solutions all failed, I will > try a brute force enumeration attack tomorrow. > > lots of fun ! > > Cheers > > Detlef > > Am 30.06.2020 um 08:37 schrieb Hal Murray: You might try the 74AC161, which > works to 73MHz at 3.3V or 103 MHz at 5V, -40 > to 85C. > Set the data inputs to DCBA = 1011 and connect an inverter from the carry > output (pin 15) to the Load input (pin 9) to divide by 5. See http:// > www.techlib.com/electronics/74161Divider.htm [1] You didn't read the data > sheet carefully enough. That 73 MHz is the bragging > number for sales people, often not useful. For something like this, you need > to add the clock-to-out for the ripple carry, prop time through inverter, and > setup time at the load input. > > I was going to ask whether 73MHz included the delay through the inverter, but > it's much worse than that. The clock to out on the RCO pin is 21 ns. Even > without the inverter, it won't make 50 MHz. > > You can save a few ns if you use a FF with inverting output instead of an > inverter. That adds a pipeline stage so you have to adjust the constant that > gets loaded. Setup time on a 3V AC74 is 4.3 ns which gets to 40 MHz (actually > only 39.5). > > At 5V, > AC161 clk-RCO is 15.2 > AC74 setup is 3.1 > So that works - 54.6 MHz. > > Using an inverter: > AC161 clk-RCO is 15.2 > AC04 prop 5.9 > AC161 setup 5.3 > That's 37.9 MHz > > (That's all assuming I didn't fatfinger anything.) > > I like Richard Karlquist's trick of using a data bit to reload. > Unfortunately, for the AC161, the data out isn't significantly faster than the > carry out. > > If I did the numbers correctly, that's 35 MHz at 3.3V and 49.3 MHz at 5V. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there. Links: ------ [1] http://www.techlib.com/electronics/74161Divider.htm _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
