Use a USB-6002 to simulate a button press

[wsmck]

I have a USB-6002 I would like to connect to a MAX6816 switch debouncer to simulate a button press for testing, and would like to leave the physical button in place in the circuit so that either the physical button or the USB-6002 could generate a button press.  To do this I need the USB-6002 DIO line in a high impedance state.  The MAX6816 has a very weak pull-up, in the 100kOhm range.   If I understand the USB-6002 digital input specs correctly, there's a 47.5kOhm pulldown in the digital input circuit.  This effectively pulls down the the MAX6816 input if I try to configure the USB-6002 DIO as an input or tristated output.   Is there any way to get the USB-6002 to switch the 47.5k pull-down out, or to remove it from the board?   Or is there a better way to configure the USB-6002 so that I don't have to drive the DIO line high and effectively prevent the physical button in the circuit from being used?

[santo_13 · Accepted solution]

47.5k on the DI circuit is fixed on the board, no way to remove (unless you want to desolder yourself and maybe mess up normal functionality).

An easy way would be to add a tristate buffer at the output of USB-6002, this way you have control over the high impedance state.

The 47.5k pull down with the weak 100k pull off of MAX6816 presents 0.32*VDD signal at the MAX6816 threshold circuit which would keep the signal at LOW since the level may never rise above VIH to register a high.