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CAN Bus Bit Masking

CANBus Communications Decoded

Relevant Module: Worked Examples > Reverse Engineering - Steering Wheel Angle Position > Step 5: Determine Variable Scaling

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G'day guys,

Would you be able to cover bit masking, even just in writing rather than a full video?

I'm attempting to characterize the CAN Bus in a 90s Volvo, so MaxxECU can write some firmware for me.

The goal is to be able to integrate this ECU into the existing network, including driving the original gauge cluster and other modules.

I'm told that later models use bit masking to hide "update bits". In the case of the tacho, this update bit keeps the gauge alive, without it the cluster shuts off after about 3 seconds. 16 bits are available in the 2 big endian bytes of RPM data, I'm told only 12 are used for transmitting RPM data & the 13th byte is the update byte.

I guess I'd like to know what software can show masked bits in CSVs and whether there is a way to identify masked bits in other instances where they may exist and I haven't been told of their potential presence.

if you're asking how to mask bits on a csv, you can use excel for such. (bitAND is the function call)

if you're asking how to determine which bits are masked prior to a message being sent, we'll that's certainly a loaded statement nobody can really answer. Bitmasks are a way to separate bits to only look at a specific portion of them.

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