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I am confused at a mistake I currently have in my setup. I am using this Holtek keyboard controller. Note how the letter Q is produced by connection between R0 and C1 (page 19). According to the datasheet, R0 is pin 6 input, and C1 is pin 20, output.

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Now, I have a matrix where the Q button is connected to the above R0 and C1, however there's also a 1n4148 diode in series with the button that is oriented from R0 to C1. I would expect this not to work, because C1 is an output pin during the matrix scan, and R1 is an input pin. The diode is reversed with respect to the flow of current (from C1 to R0). Strangely enough, it does work, and this really is the core of the question.

Is there something in the datasheet I am misunderstanding?

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    \$\begingroup\$ I recommend that you post the essential part of the linked document into your question so that we can understand the question on its own. That way you will get more readers and the question will still make sense when the link dies. \$\endgroup\$ – Transistor Jan 1 at 15:48
  • \$\begingroup\$ @Transistor it's a PDF. screenshots are going to be large \$\endgroup\$ – Stefano Borini Jan 1 at 17:30
  • \$\begingroup\$ @StefanoBorini You should learn how to crop and resize graphics. Can you please add a schematic showing how the button and diode are connected? \$\endgroup\$ – Elliot Alderson Jan 1 at 18:16
  • \$\begingroup\$ "I have a matrix where the Q button is connected to the above R0 and C1, however there's also a 1n4148 diode in series with the button ..." Is this something you are making or something you have reverse engineered? Diodes are often used in keyboard and LED matrices to prevent backfeeds when two or more keys are pressed but I would expect that this controller should be able to detect and manage that. In addition, the keyboard should be able to handle multi-key presses (Shift-X, Ctrl-Alt-Del, etc.). Where did the diodes come from? \$\endgroup\$ – Transistor Jan 1 at 18:38
  • \$\begingroup\$ @Transistor the diodes come from the fact that I am reusing a matrix I made for a different controller, for testing purposes. Now I am creating a new matrix with the connections for the Holtek, but as I was checking my old matrix to add the diodes to the new one, I noticed that the diode is reversed for the expected need of the holtek \$\endgroup\$ – Stefano Borini Jan 1 at 19:15

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