[time-nuts] Follow-up question re: microcontroller families

Hal Murray hmurray at megapathdsl.net
Sun May 26 20:17:46 EDT 2013


bownes at gmail.com said:
> For making a blinking LEDs, it is hard to beat a 74LS74. However, a PIC, is
> probably less expensive! :) 

Thanks.  :)

I was going to send a wise-ass comment, but then I checked some numbers.

Digikey, one-off DIP pricing:
  $0.62 SN74LS74
  $0.55 PIC10F200
  $0.33  SN74HC74

So technically you are correct, but only because you are picked an ancient 
technology.

Besides, the '74 needs a clock while the PIC has an internal clock calibrated 
to 1%.

I suspect what's going on is that the '74 is pad limited(*) so you are paying 
per-pad rather than per gate.  The PIC only has 8 pins, so if it's close to 
pad limited it will be cheaper.

The PIC10F200 has 3 output pins so it can blink 3 LEDs independently while 
the '74 only has 2 FFs.

High volume (whole tape, 2-3K) prices are $0.34, 0.22, and 0.10

------

*) If you aren't familiar with pad-limited, it's a cool idea.  Consider a 
chip that has N pins.  Each pin needs a pad for the bond wire.  Arrange those 
in a rectangle around the perimeter of your chip.  That leaves a hole in the 
middle.  Put your logic in there.  If it doesn't fit, push the pads out until 
there is room.  That makes your chip bigger and more expensive.  If it fits 
with room leftover, you can add more logic for free.  That's why low cost 
watches have so many features.


-- 
These are my opinions.  I hate spam.





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