AB ML1500 to Emerson servo over ModBus

Allan Barnes

Member
Join Date
May 2004
Location
Woodstock ON
Posts
122
Has any one run into a problem where the Most significant and least signigicant words between 2 devices are different.

This seems to be my problem when writting a Long Int from the ML1500 to the Emerson Ei-203.

In my ML1500 I use a "CPW" to move my data from Longs into Intagers, swap the MS wors with the LS word, then send them off to the servo.

For my feedback from the servo I do the same but in the reverse direction.

This works great untill I have Negative Number, then the Index Distance I have sent my servo goes all waky, and the servo makes a very long index.

Note: the data type in the servo is definetly a Signed 32bit integer

Any help would be greatly appreciated.
 
Ok so I dug a little deeper.
Turnes out when I use the CPW function to turn the 1 long integer word into 2 integers, the CPW only writes to the first integer and not the second integer.

So because the Second words is All 0 at the bit level my servo distance is all wonky.

SO how do I move the Long into 2 ints and keep all the bits in both the MS Word and the LS word.

Going from 2 ints to 1 long seems to work flawlessly (hopefully by saying that I do not activate a curse)
 

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