Most CPUs have assembly instructions called something like "shift left/right" or "rotate left/right". That implies an endianness, and it is (to my knowledge) always the endianness of normal written numbers - most significant is "left". That is, big endian.
Bit-endianness is only relevant for serial transmission. You only have to worry about it in circumstances where you have hardware that assumes a different bit order than what you're communicating with. Otherwise, the internal layout of words is abstracted and you can ignore it.
It's relevant when dealing with the control registers of peripherals, even if that's over a parallel bus. It's at least important that you have the same bit order as the peripheral.
Comments
Most CPUs have assembly instructions called something like "shift left/right" or "rotate left/right". That implies an endianness, and it is (to my knowledge) always the endianness of normal written numbers - most significant is "left". That is, big endian.
Bit-endianness is only relevant for serial transmission. You only have to worry about it in circumstances where you have hardware that assumes a different bit order than what you're communicating with. Otherwise, the internal layout of words is abstracted and you can ignore it.
It's relevant when dealing with the control registers of peripherals, even if that's over a parallel bus. It's at least important that you have the same bit order as the peripheral.