[time-nuts] low power divide by 5

[dschuecker]

hm,

first example of divide by 5 needs an additional AND, second example 
gets stuck in an unused state :(

Cheers

Detlef

Am 01.07.2020 um 02:14 schrieb David:
> 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 at 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 at lists.febo.com
> To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> and follow the instructions there.
>