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This property should contain a comma-separated list of I/O line numbers, for example: "28, 30, 31". Line numbers correspond to those of the pl_io_num enum. This enum is platform-specific. The declarations for the pl_io_num can be found in the "Platform-dependent Constants" section of your device's platform documentation (for example, EM1000's is here).
The kp.scanlinesmapping string should only contain a list of decimal numbers. That is, use "28" and not "28- PL_IO_NUM_28". Only numerical characters are processed anyway — writing "28- PL_IO_NUM_28,30-PL_IO_NUM_30" will set this property to "28,30". You can, of course, use the following way as well:
The order in which you list the scan lines does matter — this is the order in which the lines will be numbered. The order of scan lines listed in this property directly influences the formation of key codes.
This property can only be changed when the keypad is disabled (kp.enabled= 0- NO). Setting the property to "" means that the keypad will have no scan lines, which is also a valid keypad configuration.
Scan lines of the keypad should be separate from the return lines (see kp.returnlinesmapping). The keypad will not work properly if you designate any I/O line as both a scan line and a return line.
Scan lines are only required if you are working with a matrix keypad.