Controllogix, J1939, Two's Complement

[Ken Roach]

The Masked Move instruction is more like a Masked Copy: the source and destination are the same size and only the masked bits are transferred to the destination.

I put a zero into the Destination tag prior to the Masked Move mostly out of habit, because if a value greater than 255 gets into that destination tag at some point, the high bits won't be written over by the Masked Move and can mess up the math and confuse the troubleshooter. I've had this happen in logic that was otherwise flawless when I absentmindedly entered a constant into a tag.

The MOV instruction is more general-purpose and as noted by other posters, it preserves the *value* of a tag, not the bit pattern.

I don't know how that bit designator got there; you're right and the source is AB7645:I.Data[9]

 

[Ken Roach]

The number of bytes copied by the COP instruction is determined by the destination tag datatype.

If you're copying from an array of INTs into a DINT, the COP length (LEN) of 1 copies 4 bytes, which is 2 INTs.

I have used the MVI56-MCM quite a bit, but never the "swap" feature. I think it swaps bytes, not words.

 

[Kyle Grathwol]

Kyle, thanks for the info. If your working on Caterpillar Gensets, and need anything feel free to email me - [email protected]

Please check your spam folder. I sent you an e-mail this morning.