3-state buffer with > 4 gates?

Discussion in 'General Electronics Chat' started by philbowles2012, Jan 18, 2014.

  1. philbowles2012

    Thread Starter New Member

    Mar 28, 2013
    23
    1
    There seem to be plenty of buffer chips (both inverting and non) that have more than 4 gates, but they are all active at once... I need individually controlled gates as in the 74HC125

    I'd be equally happy with switches as in the 4066 - essentially I want to "tri-state" 16 different lines...quad-gate chips will require 4 separate chips,
    hex (if I could find one) would require 3 (with 2 unused) and an octal (INDIVIDUALLY CONTROLLED) would only need 2.

    I think there ought to be such a beast, in 28-pin...in,out,enable x8 = 24 pins leaving Vcc GND and 2x NC

    Any suggestions?
     
  2. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    Are you going to connect this to a microcontroller?

    Microchip.com make a "port pin expander IC" which can be controlled by 3 SPI wires, and has a lot of pins that can be configured as in/out/tristate.
     
  3. philbowles2012

    Thread Starter New Member

    Mar 28, 2013
    23
    1
    I hadnt planned on using mcu...wanted it all hardwired, but your remark has got me thinking....do you know the chip part number?
     
  4. ScottWang

    Moderator

    Aug 23, 2012
    4,850
    767
    What are you trying to do for those ic?

    CD4051,CD4052,CD4053 -- CMOS Analog Multiplexers/Demultiplexers
    with Logic Level Conversion

    A lots of analog switches here.

    I have been used the CD4051 and CD4066 to measuring the voltage.
     
  5. philbowles2012

    Thread Starter New Member

    Mar 28, 2013
    23
    1
    none of those mux chips comes close I need 16 lines thta can be individually set to high impedance z state.

    as per my first post, 74hc125 does exactly what I want, but only has 4 gates. my current design therefore needs 4 of them. iim trying to reduce the chip count.

    the 16bit io expander sounds like a good one, just need to get my head around the difference ((if any) between high-impedance and open drain/collector.

    if it helps, I have a zif socket into which I want to drop a variety of different chips, with very different pinouts, e.g. pin 1 might be Vcc on one chip but CLK on another. in some cases, the pin MUST have no connection. so I have some gate logic which routes one of 6 signals to the appropriate socket pins, and all the other pins need to appear if there is nothin connected to them...

    the plan is to have every pin fed from a 3-state buffer, which is fed by the signal logic as input, and also sets OE on the buffer to either feed the selected signal to the pin or set it to Z ie make it appear as if the pin is NC.

    hope this explains it.

    as I understand it, open collector will float if not pulled up or down. obviously up or down is no good to me as it will appear to the chip as an input of some kind...the situation I have to avoid is where the chip drives the incoming gate backwards and fries the input logic. a 4066 would work as it would be truly open circuit but I think it cant pass enough current when its conected, hence my need for buffer that can be similarly open-cicuited
     
  6. crutschow

    Expert

    Mar 14, 2008
    12,974
    3,220
    For 5V maximum, this matrix switch, which is available in an 8X8, may work for you. It has 2.5Ω ON resistance. But it does have a serial interface which would require some logic, such as an 8-bit parallel-in serial-out shift register per chip plus some timing logic, or a μP to control the chip address.
     
  7. ScottWang

    Moderator

    Aug 23, 2012
    4,850
    767
    This chip already list on the website that I linked, but he just want to find the pure hardware control first.
     
  8. philbowles2012

    Thread Starter New Member

    Mar 28, 2013
    23
    1
    some grat ideas and advice. im going to go with 4x4066 first and prove the theory and the logic. once its working, vn2.0 will replace the logic chips with a uP contoller driving one of the chips/expanders you guys suggested...and of course a sexy ui instwad of 4 dip switches for input,

    for info its an attinyxxx programmer with a single 28pin zif socket. the idea is you can drop any avr attiny into the zif, select which pinout type it is and then upload code. should work with 13,25,45,85 24,44,84 26,261,461,861 2313,4313 48,88 and also mega8,168,328 etc...plus any other mcu that has same SPI,Vcc, GND pins as any of the above.
     
  9. ScottWang

    Moderator

    Aug 23, 2012
    4,850
    767
    Last edited: Jan 19, 2014
Loading...