ProgrammingPage 5-4 ABB Control - AC 311SBC 260400 R1001-b 06.992. List of variablesThere 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 theintermediate calculations. The indirect bit, word or double word constants. The chain steps: a chain step enables running sequential operations. Each chain stepenables 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 cyclesin order to execute. A historical value is an internal register used by this type of function tostore 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 seriescentral 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 ofthe other functions. The number of authorized timer functions is unlimited, however thenumber of simultaneous timer functions is limited to 42.
