help finding digital SSI chips

Discussion in 'The Projects Forum' started by luck, Feb 21, 2008.

  1. luck

    Thread Starter New Member

    Jan 25, 2008
    I need two latching chips (or one that does both things).

    The first needs to latch when an input signal goes high, and keep that high signal as an output. So I want to have the output from the latch to be low before the latch triggers, then once the latch triggers I want the output to be high until the latch is reset.

    The second thing I need is a latch that will take two changing inputs and will output the same value until the latch triggers at which point the outputs will remain the same (same as the input when the latch was triggered) regardless of the changing input. Again it needs to hold this value until the latch is reset.

    So the difference is the first will use the input as the trigger while the second will use an external trigger. You may be able to do both with the same chip but I am not sure if I would hit a timing problem in the first by using a signal as its own trigger.

    Again I am looking for these functions in the form of SSI chips, and I really don't have any idea on where to began looking for them. Any help would be appreciated.
  2. scubasteve_911

    Senior Member

    Dec 27, 2007
    For the sake of clarity, are you able to make a truth table of what you want? It's exhausting interpreting english to logic :)

  3. SgtWookie


    Jul 17, 2007
    This sounds like a homework problem.

    Is it?

    I will give you a hint: NAND is what you seek.
  4. luck

    Thread Starter New Member

    Jan 25, 2008
    This is not for homework, it is part of a side project for making three buzzers for a trivia type game that will tell you what order they were pushed.

    For the first one (triggered when I goes high for the first time)
    T I O (T is triggered, I in input, O is output)
    0 0 0
    0 1 NA
    1 0 1
    1 1 1

    For the second one (triggered at time 2)
    T I1 I2 O1 O2
    0 x1 y1 x1 y1
    1 x2 y2 x2 y2
    1 x3 y3 x2 y2

    I also may be miss using the term SSI chip, I am looking for a small chip that does just this function, I am not looking to build these functions out of NAND and NOR gates.
  5. SgtWookie


    Jul 17, 2007
    Oh, ok - then you want VLSI (Very Large Scale Integration) IC's - because SSI (Small Scale Integration) is just the basic gates.

    Your cheapest route would likely be a PIC microcontroller or similar.

    The MPU, resonator, power supply, LCD display, and lotsa buttons.

    Easier to use NC buttons than NO. That way, you won't have to deal with debouncing.