3 ms·

That is the aforementioned switching power supply. On the other hand what I see as more funky is IC1 and IC02, what exactly is that? Some kind of gated compara

by dfox 9y ago

That is the aforementioned switching power supply. On the other hand what I see as more funky is IC1 and IC02, what exactly is that? Some kind of gated comparator? (Also of note is how IC3A and B has different, but equivalent, logic symbol to IC3C and D)

kens 9y ago
IC1 is a 75140 dual line receiver, where pin 6 is a reference and pin 2 is a strobe, so pretty much what you thought. Also of interest is IC101, a 75122 triple line receiver, which has a Schmitt trigger, two AND gates and a NOR for each line. Most of the pins are tied to ground (1, 2, 3, 4, 12) so it's used as a buffer, ignoring the rest of the logic. For IC3A-D, I think what's going on with the symbols is a briefly-popular way of representing positive logic and negative logic by changing the symbols so a wire has bubbles on both ends. In other words, if you have active-high inputs, represent it as a NAND gate, but if you have active low inputs, represent it as an OR gate with inverters on the inputs. It's the same gate, just drawn to indicate if it's performing an AND or OR. Note the way the bubbles move on the inverters too.
- bsder 9y ago
  Well, IC3A and IC3B are just functioning as inverters ... The thing with the bubbles is probably an old technique that we used to use called "pushing circles". You can shove all the circles on one side of a logic gate to the other side of the logic gate by exchanging the gate type (AND->OR, OR->AND). And then you can ignore lines with two bubbles in series (ie. a double inversion). There are a bunch of tricks that we used to use when you had to do everything on graph paper. It's actually a good thing that they are lost to the mists of time as it means we have progressed enough that they don't matter anymore.
  - thrownhwn 9y ago
    Cool, had to Google bubble pushing[1] [1] http://district.bluegrass.kctcs.edu/kevin.dunn/files/Simplification/mobile_pages/4_Simplification10.html http://district.bluegrass.kctcs.edu/kevin.dunn/files/Simplif...

by dfox 9y ago

kens 9y ago

IC1 is a 75140 dual line receiver, where pin 6 is a reference and pin 2 is a strobe, so pretty much what you thought. Also of interest is IC101, a 75122 triple line receiver, which has a Schmitt trigger, two AND gates and a NOR for each line. Most of the pins are tied to ground (1, 2, 3, 4, 12) so it's used as a buffer, ignoring the rest of the logic. For IC3A-D, I think what's going on with the symbols is a briefly-popular way of representing positive logic and negative logic by changing the symbols so a wire has bubbles on both ends. In other words, if you have active-high inputs, represent it as a NAND gate, but if you have active low inputs, represent it as an OR gate with inverters on the inputs. It's the same gate, just drawn to indicate if it's performing an AND or OR. Note the way the bubbles move on the inverters too.

bsder 9y ago
Well, IC3A and IC3B are just functioning as inverters ... The thing with the bubbles is probably an old technique that we used to use called "pushing circles". You can shove all the circles on one side of a logic gate to the other side of the logic gate by exchanging the gate type (AND->OR, OR->AND). And then you can ignore lines with two bubbles in series (ie. a double inversion). There are a bunch of tricks that we used to use when you had to do everything on graph paper. It's actually a good thing that they are lost to the mists of time as it means we have progressed enough that they don't matter anymore.
- thrownhwn 9y ago
  Cool, had to Google bubble pushing[1] [1] http://district.bluegrass.kctcs.edu/kevin.dunn/files/Simplification/mobile_pages/4_Simplification10.html http://district.bluegrass.kctcs.edu/kevin.dunn/files/Simplif...