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I am trying to write keypad (4*4) scan VHDL code for my DE10-lite board. In order to avoid floating signal for the input, I need pull up resistors.

enter image description here

There is an example I found from YouTube

However, the keypad only has 8 pins. How can I connect Vcc with pull up resistors to it?

enter image description here

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  • \$\begingroup\$ So the FPGA has no built-in pull-ups or pull-downs? \$\endgroup\$
    – Justme
    Commented Feb 17, 2023 at 22:21
  • \$\begingroup\$ the keypad only has 8 pins ... why do you say only? ... the schematic diagram shows 7 pins ... your keypad has more pins than the schematic \$\endgroup\$
    – jsotola
    Commented Feb 17, 2023 at 23:11
  • \$\begingroup\$ @jsotola I use 4*4 keypad \$\endgroup\$
    – kile
    Commented Feb 20, 2023 at 8:34
  • \$\begingroup\$ the schematic diagram shows pullup resistors on all of the MCU input and output pins ... you connect the resistors the same way on your keypad \$\endgroup\$
    – jsotola
    Commented Feb 20, 2023 at 13:40

2 Answers 2

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The simple answer to your question is to re-draw it with the pull-up resistors at the other ends of the rows and columns. It's electrically the same, but now the resistors can be connected to the pins.

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  • \$\begingroup\$ Can you provide me a simple diagram as an example? \$\endgroup\$
    – kile
    Commented Feb 20, 2023 at 9:20
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If you have 4x4 keypad as shown in figure, this is how it looks internally enter image description here

connect the pins 1-r1, 2-r2, 3-r3, 4-r4, 5-c1, 6-c2, 7-c3, 8-c4, there is no need of pull-ups. but if you want, you can connect four 10k resistors from r1,r2,r2,r4 to Vcc.

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  • \$\begingroup\$ I tried this. It doesn't work. The following from this link is working learn.parallax.com/tutorials/language/propeller-c/… \$\endgroup\$
    – kile
    Commented Feb 20, 2023 at 8:36
  • \$\begingroup\$ @kile, It depends on how you write the scanning algorithm \$\endgroup\$
    – Chr_arj
    Commented Feb 20, 2023 at 8:56
  • \$\begingroup\$ How do you avoid floating signal of GPIO without resistors? \$\endgroup\$
    – kile
    Commented Feb 20, 2023 at 9:20
  • \$\begingroup\$ @kile, simply by connecting some pull ups or pull down resisitors, also i can use internal pull ups if present. \$\endgroup\$
    – Chr_arj
    Commented Feb 20, 2023 at 9:22

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