I'm testing the SN76489AN chip with Arduino and I'm able to play the 3 tones I want etc BUT I don't understand why the READY pin is not working? The datasheet says the pin goes high when the chip is ready and low when it's busy with processing a command. But the READY pin is always low! I've got 2 brand new pieces of the chip and they both act this way. I've even tried to pull-up this pin but it didn't help. I see everyone is just using delayMicroseconds in their examples, so I guess it is a common problem but it's just strange... Is it a bug in the chip or what? Does anyone know?


  • Please post a link to the datasheet for the chip. How do you know the pin is always low? Do you measure it (and if so, how?), or is it a side-effect of the code? If the latter, please post your code using the code formatting markdown (four leading spaces). For help see Markdown help. You should be able to do this by selecting the code and pressing Ctrl+K to have your browser do this for you.
    – Nick Gammon
    Commented Feb 26, 2016 at 22:24
  • 2
    READY is open-collector. It will require a pullup-resistor. Test circuit in datasheet shows a 2kohm resistor. Commented Feb 26, 2016 at 22:25
  • Oh, so the pull-up idea was good, but I just used too big resistor. I haven't noticed the 2K resistor in the test circuit! Thanks @Mikael! (sorry I can't give you +1 here yet). Unfortunately this method is not much fuster than the version with delay. PS: @Nick, I have measured it when the chip was idle (when it should by high) and I am actively waiting for the pin to become high in a while loop.
    – P.W.
    Commented Feb 26, 2016 at 23:19
  • @MikaelPatel, if you will copy your comment as an answer then I will be able to mark it as answer and close the question.
    – P.W.
    Commented Feb 26, 2016 at 23:34

2 Answers 2


The READY signal is open-collector. It will therefore require a pullup-resistor. Test circuit in datasheet shows a 2 kohm resistor. You could try with that. Alternatively use the internal pullup resistor on the input pin but this may be too large (weak).



I had this problem, but the mistake was that I had missed the clock pin on my breadboard by one row, so there was no clock signal.

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