Spin Language Qeustion

hylee101001

I'm working with mpu. From an I2C library, I have experienced an over-flow-looking-like numbers when I had this:

mpuRawData[0] := (I2C.read(mpuAdd, mpuXAccH)<< 8) | (I2C.read(mpuAdd, mpuXAccL) & $ff)

But I have added this second line (because I saw this from another I2C library)

~~mpuRawData[0]

And numbers are clean!

Q1. Does someone know what the second line do? Is it somehow related to 2's complement conversion?

Q2. What does "&$ff" do form the first line?( it looks somehow attaching a 0 at the end of line. though..)

Cluso99

(I2C.read(mpuAdd, mpuXAccH)<< 8)
This takes the value returned from the call I2C.read(mpuAdd, mpuXAccH) and shifts it left 1 byte (8 bits)

(I2C.read(mpuAdd, mpuXAccL) & $ff)
This takes the low byte (8 bits) of the call I@C.read(mpuAdd, mpuXAccL) by ANDing the result with $FF.

Then the two results are ORed together.

JonnyMac

Does someone know what the second line do? Is it somehow related to 2's complement conversion?

That second line converts a 16-bit signed number into a signed long (the native type for Spin). See page 157 in the manual.

Q2. What does "&$ff" do form the first line?( it looks somehow attaching a 0 at the end of line. though..)

The & $FF is unnecessary because an I2C read returns 8 bits hence is already limited to 0..255