Introduction to Bitmasking

Bitmasking is a method used to manipulate individual bits of a binary number by applying bitwise operations with a mask. A mask is a binary number designed to target and select specific bits from another binary number.

Example that extracts four different statuses from the same byte

In all the examples, we´ll use the failure status bit 0x21. It´s position in the raw BLE Advertising Frame is marked with pink color.

0x0201060A0957454D46464646354410FF0E0421114948490000000000005400

Byte Failure Status table

Mask	Masked Byte Value	Extracted Bit Values	Description	Comment
0x30 0011 0000	0x00 0x10 0x20 0x30	0 1 2 3	Battery extreme low Battery Low level Battery OK No data	Battery level
0x03 0000 0011	0x00 0x01 0x02	0 1 2	No Data No failure Failure	Wheel End Failure
0xC0 1100 0000	0x00 0x40 0x80 0xC0	0 1 2 3	No failure Piezo Failure WEM Failure Reversed position	WEM failure = accel or RAM failure

In TraX, we have the following bitmasks: 0x30, 0x03, 0xC0, and 0x0C. These hexadecimal values represent specific bit patterns.

Masking for Different Failures

Battery Level Mask 0x30

To apply the bitmask, we perform a bitwise AND operation between the byte and the mask:

  0x21 (00100001)
& 0x30 (00110000)
= 0x20 (00100000)

Result: Applying the 0x30 bitmask to 0x21 is 0x20, indicating "Battery OK".

Wheel End Failure Mask 0x03

  0x21 (00100001)
& 0x03 (00000011)
= 0x01 (00000001)

Result: Applying the 0x03 bitmask to 0x21 gives 0x01, indicating No Wheel End Failure.

WEM Failure Mask 0xC0

  0x21 (00100001)
& 0xC0 (11000000)
= 0x00 (00000000)

Result: Applying the 0xC0 bitmask to 0x21 gives 0x00, indicating No WEM Failure.

Temperature Sensor Failure Mask 0x0C

  0x21 (00100001)
& 0x04 (00001100)
= 0x00 (00000000)

Result: Applying the 0x0C bitmask to 0x21 gives 0x00, indicating No Temperature Failure.

Javascript Code Sample

See the file "bit-masking-example.js" attached to this article.