List Of Variables - ABB AC 31 Technical Manual

2. List of variables

Page 5-4
Programming
There are 5 types of variables used in the user program:
The physical, binary or analog, Input / Output variables
The internal bit, word or double word variables used in the user program for the
intermediate calculations.
The indirect bit, word or double word constants.
The chain steps: a chain step enables running sequential operations. Each chain step
enables the definition of a step. One single step may be active at a time.
The historical values: certain functions require the execution of numerous program cycles
in order to execute. A historical value is an internal register used by this type of function to
store the result, of the function, in the program cycle n-1 during the functions process.
The historical values are not directly accessible, in the user program, with the 40 and 50 series
central units.
Comments on the historical values:
The maximum number of historical values allowed in a project is 256.
A list of the functions and their historical values is available in the annex.
The historical values of the timer functions are independent from the list of historical values of
the other functions. The number of authorized timer functions is unlimited, however the
number of simultaneous timer functions is limited to 42.
ABB Control - AC 31
1SBC 260400 R1001-b 06.99