Loading ...
Sorry, an error occurred while loading the content.
 

Re: [cosmacelf] Re: Cosmac Elf on breadboard troubles

Expand Messages
  • David W. Schultz
    ... If you mean pin 12 of the 4013, yes. Pressing the input button toggles the clock pin of the 4013 dual D flip flop. Since its D input is tied high, the notQ
    Message 1 of 51 , Mar 3, 2012
      On 03/03/2012 10:21 AM, alkopop79 wrote:
      > Yeah, I didn't think the pic would help... What makes debugging hard
      > is that I have faint ideas how the supporting logic circuit works.
      > For instance, in LOAD mode, when I press the input button, should the
      > flipflop 4013 change state of Q output?
      >

      If you mean pin 12 of the 4013, yes.

      Pressing the input button toggles the clock pin of the 4013 dual D flip
      flop. Since its D input is tied high, the notQ output (pin 12) will go
      low. When the 1802 performs a DMA cycle the SC1 output will go high and
      this asserts the reset pin of the 4013 bringing the notQ output high.

      >Is it a good idea to ground all the floating pins?

      It is critical. If you leave a CMOS input floating it can result in very
      high current draw and flaky operation. Note that the 4013 is shown with
      pins 3 to 8 tied to ground. This is power, the SET input of the flip
      flop being used, and all the inputs for the unused flip flop.


      --
      David W. Schultz
      http://home.earthlink.net/~david.schultz
      "Who? What? Where? When? Aahhhg!" - Duck Dodgers
    • David W. Schultz
      ... Those pins are connected to /MREAD and /MWR. When you request a DMA-IN cycle you get a memory write cycle where your peripheral must provide the data.
      Message 51 of 51 , Mar 17, 2012
        On 03/17/2012 10:49 AM, alkopop79 wrote:
        > Can you guys tell me what should be the state
        > of pins 18 and 20 (output disable and write enable) in run and load
        > mode and when pressing the input button? The datasheet doesn't have
        > much info on this.

        Those pins are connected to /MREAD and /MWR. When you request a DMA-IN
        cycle you get a memory write cycle where your peripheral must provide
        the data. (machine cycle type no. 7 in the 1802 data sheet, ca. 1979)



        --
        David W. Schultz
        http://home.earthlink.net/~david.schultz
        "Who? What? Where? When? Aahhhg!" - Duck Dodgers
      Your message has been successfully submitted and would be delivered to recipients shortly.