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How to connect a keypad to your Armadeus board


Your Armadeus board allows you to connect a (matrix or not) keypad as input device. Keypads are a collection of switches assembled together to emulate a kind of keyboard to ease user interaction with your system.


There are several solutions to connect a keypad to your Armadeus board:

Keypad directly connected to i.MXL/27

One GPIO for one key

This type of keypad generally called "common ground keypad" is the easiest one to build: connect your switch to an i.MX GPIO (with a pullup) on one side and to the ground on the other side . If you need more than 6 keys, this construction is however "GPIO consuming" and you would better use matrix keypads.
Under Test...

Matrix keypads on i.MX27

The i.MX27 has an internal controller that can drive 8x8 keypads (= 64 keys with 16 dedicated pins): Keypad usage on i.MX27. Please consult the i.MX27 Reference Manual (Chapter 25) for more informations.

Matrix keypads on i.MXL

Driver for i.MX GPIO controlled keypads

By default your board supports a direct connection with a 4x4 matrix keypad using the CSI lines: CSI_MCLK, CSI_D0...CSI_D6.

The driver uses the i.MXL GPIO's internal pull-up, therefore your board does not need any additional external resistor.

  • Connect the 4 (rows) lines of the keypad to CSI_MCLK, CSI_D0, CSI_D1, CSI_D2 (resp. PORT_A pin 3, 4, 5, 6)
  • Connect the 4 (columns) lines of the keypad to CSI_D3, CSI_D4, CSI_D5 CSI_D6 (resp. PORT_A pin 7, 8, 9, 10)

{add a big picture of the keypad link with APF_DEV_LIGHT} {add a big picture of the keypad link with APF_DEV_FULL}

3x4 matrix keypad connected to i.MX GPIOs
Keypad Connection (APF9328_devfull)
4x4 keypad caracters and corresponding CSI signals
CSI signal name D6 D5 D4 D3
X23 pin number 7 8 5 6
MCLK 14 1 2 3 <-
D0 1 4 5 6 ->
D1 4 7 8 9 ENTER
D2 3 * 0 _ ESC

FPGA solution

Development are also ongoing to connect matrix keypads using the FPGA...


Quick try

  • If you have a graphical LCD connected to your board (= virtual terminal), then you should see what you type (if your keypad keys are mapped to alphanumeric keyboard keys).
  • If you don't have any virtual terminal, but only the serial console: (event0 may be event1 if you already have a running touchscreen)
# cat /sys/class/input/input0/event0/device/name       (check if event0 is really attached to keypad, otherwise, try event1, etc...)
MX27 Keypad
# cat /dev/input/event0

Then you should see weirds characters when pressing keyboard keys:

 �,~~_�,}�}�3T,QToT6,TT�,�;��, � �
  • if the test wiped out your console, you can get it back with:
# reset
  • if you want to see hexadecimal values of what your are receiving:
# cat /dev/input/event0 | hexdump
0000000 0283 0000 5a09 000e 0004 0004 0051 0007
0000010 0283 0000 5a30 000e 0001 006c 0001 0000
0000020 0283 0000 5a40 000e 0000 0000 .... ....
  • If corresponding device node in /dev/input/ is not existing, then:
 # cat /sys/class/input/input0/event0/dev
 # mkdir -p /dev/input
 # mknod /dev/input/event0 c 13 64

Deeper one

  • use target/demos/keypad_test/ test tool

«standard» one

By default, keyboard are connected on /dev/tty1. Then to read keyboard output, simply cat on /dev/tty1 (type enter to see the text line):

# cat /dev/tty1



evtest is a tool already installer on bsp to test keys comming from /dev/eventX. To use it simply launch it with path to device :

# evtest /dev/input/event1 
Input driver version is 1.0.1
Input device ID: bus 0x19 vendor 0x1 product 0x1 version 0x100
Input device name: "gpio-keys.5"
Supported events:
  Event type 0 (EV_SYN)
  Event type 1 (EV_KEY)
    Event code 21 (KEY_Y)
    Event code 49 (KEY_N)
Testing ... (interrupt to exit)
Event: time 201.720156, type 1 (EV_KEY), code 21 (KEY_Y), value 0
Event: time 201.720156, -------------- SYN_REPORT ------------
Event: time 202.040401, type 1 (EV_KEY), code 21 (KEY_Y), value 1
Event: time 202.040401, -------------- SYN_REPORT ------------
Event: time 202.580177, type 1 (EV_KEY), code 49 (KEY_N), value 0
Event: time 202.580177, -------------- SYN_REPORT ------------
Event: time 202.930185, type 1 (EV_KEY), code 49 (KEY_N), value 1
Event: time 202.930185, -------------- SYN_REPORT ------------


showkey is already installed on armadeus bsp. It display all event (press or release) on key with codes :

# showkey 
kb mode was UNICODE
[ if you are trying this under X, it might not work
since the X server is also reading /dev/console ]

press any key (program terminates 10s after last keypress)...
keycode  21 press
keycode  21 release
keycode  22 press
keycode  22 release
keycode  28 press
keycode  28 release
keycode 105 press
keycode 105 release


kbd is most advanced package that can be selected in config :

Target packages  --->
    Hardware handling  --->
        [*] kbd

Some program are provided with kbd.


To change keyboard mode. To see actual mode symply type without arguments:

# kbd_mode
The keyboard is in the default (ASCII) mode

Mode can be change with options :

  • -s: scancode mode (RAW),
  • -k: keycode mode (MEDIUMRAW),
  • -a: ASCII mode (XLATE),
  • -u: UTF-8 mode (UNICODE).

Read more at: [1]






  • external links (for exemple: locomo driver model)