Error messages from the local axis control micros
	

  The servo execution program communicates with the control VAX via
an up- and a down list. The uplist contains a requested state, the
Taylor series for the position and an error quit entry. The down list
contains the the indicated position, the commanded - indicated error an 
currently the real-time clock stamps, all in a ring buffer of 50 entries.
The ring buffer is preceeded by a pointer area, which also contains one
entry for the program state and one entry for error conditions.
To identify an error, a bit position is assigned to each error condition.
In case of such a condition, the bit is ored to the error entry; the
program executes about 40 times between communicating with the control VAX, thus
no error condition is lost. 
  Upon receiving a valid up-list, (the check sum of the list is correct and the
time for the list is valid ) the error quit is investigated. If a bit
is set in the error quit entry from the VAX, the same bit is cleared in the
error entry. From now on further error conditions will be collected.
  The error condition (and also error quit) is a 16 bit entry. The following
list of the error conditions gives the hex word and the corresponding
error condition.
Communication errors:
	0001	Up-list check sum error

Problem with the commanded tracking curve
	0010	Acc in the list (or in the tracking curve) is too big
	0020	Velocity in the list  (or in the tracking curve) is too big
	0040	Position step between lists (or in the traking curve) is big

Limit conditions
	0100	Position below software limit
	0200	position above software limit
	0400	Real time clock step not is not equal to 1

Safety shutdown
	0800	Hardware pre limit is encountered
	1000	Safety check encounteres too many jumps in commanded output


				J.B.Schraml, June 94