Using 24 inputs of an Arduino Micro?

Other Hardware 3rd Party Boards
1

TL;DR:
Can I use PB1, PF4, PF6, PC7, PB0, PD2, PD0, PC6, PE6, PB5, PB7, PB3, PF0, PF1, PF5, PF7, PB2, PD3, PD1, PD4, PD7, PB4, PB6, PD6 as digital inputs for the following Pro Micro?

More details:

I'm replacing the original controller on my Filco Minila keyboard by a Pro Micro controller running this (ml67/02-circuit.md at master · jonhiggs/ml67 · GitHub).

However, I don't want to compress the existing matrix and therefore I need a controller with 24 inputs (the keyboard matrix has 8 rows and 16 columns, besides the GND and 5V).

I bought a Pro Micro exactly like this one (http://www.pighixxx.com/test/pinouts/boards/micro.pdf) which says it has 24 Port Pin, each corresponding to a Physical Pin, so I thought it was exactly what I needed. The pinout I devised, using the 24 inputs, is the following:

               _____________
  PB1 SCK  <-- | C13 | GND | --> GND
  No need  <-- | D.1 | C12 | --> MISO PB3
  No need  <-- | D.2 | C11 | --> A5   PF0
       5V  <-- | 5V  | C10 | --> A4   PF1
  PF4  A3  <-- | C15 |  C9 | --> A2   PF5
  PF6  A1  <-- | C14 |  C8 | --> A0   PF7
  PC7 D13  <-- | R7  |  C7 | --> MOSI PB2
  PB0  SS  <-- | R6  |  C6 | --> TX1  PD3
  PD2 RX1  <-- | R5  |  C5 | --> D2   PD1
  PD0  D3  <-- | R4  |  C4 | --> D4   PD4
  PC6  D5  <-- | R3  |  C3 | --> D6   PD7
  PE6  D7  <-- | R2  |  C2 | --> D8   PB4
  PB5  D9  <-- | R1  |  C1 | --> D10  PB6
  PB7 D11  <-- | R0  |  C0 | --> D12  PD6
               ¯¯¯¯¯¯¯¯¯¯¯¯¯

My problem is that the documentation I read about this controller talks about 20 inputs (e.g., http://www.watterott.com/de/Arduino-Micro). Can I use all the ports I've selected above for input, since I don't want to use serial, nor I need the TX/RX leds?

Thanks in advance!

2

Safest bet is to test it.
Write a simple sketch to set all the pins as input pullup then loop read the pins back to ensure they all read high.
Then one input at a time short it to ground and see if that pin (and only that pin) reads low.

Another possible way to do what you want is use a port expander chip like this that would use 2 or 3 pins to give you another 16 I/O pins. You could daisy chain 2 or more together and still only need 2/3/4 pins on your MCU for 32 extra I/O pins.

EDIT: Other I/O expanders here

3

Bumping this because I also want 24 inputs, and I've seen on pinouts that the board has 20 (I'm using a chinese clone). SS,SCK,MISO,MOSI aren't shown as inputs.

I was going to ask about whether I should try designating the pins as digital in a config file somewhere. Backup plan was to directly read the PORTS which I just learned to do.

But, for anyone else wondering. I just tried using them as inputs and they work. Makes total sense, what I thought was a gap (pins 14,15,16,17) isn't really a gap !

Hope that helps someone.