about CASE and variable in 840Dpl CNC program?

Hi, guys, how are you?

We have an 840Dpl milling machine. There is a CNC program in workpiece file:

IF ($A_DBB[19] B_AND 1==1) GOTOF ABC

N100 REFCYCLE_12 ;AUFRUF REFERENZ-ZYKLUS
;*********************************************************************************
N110 STOPRE

ABC:

N120 IF($A_DBB[2] B_AND 2==2) GOTOF END
N130 CASE PARTNUMBER OF 1 GOTOF MIDDLE 2 GOTOF MIDDLE 3 GOTOF MIDDLE 4 GOTOF LONG 5 GOTOF MIDDLE 6 GOTOF LONG 7 GOTOF MIDDLE 8 GOTOF LONG 9 GOTOF LONG 10 GOTOF LONG 11 GOTOF LONG 12 GOTOF LONG 13 GOTOF LONG 14 GOTOF LONG 15 GOTOF LONG 16 GOTOF SHORT 17 GOTOF SHORT 18 GOTOF SHORT_AWD 19 GOTOF SHORT 20 GOTOF SHORT 21 GOTOF MIDDLE_620 22 GOTOF MIDDLE_620
;*********************************************************************************
N140 FAULT:MSG("WRONG PART ")
N150 M0
N160 GOTOB FAULT
;*********************************************************************************
N170 SHORT:
N180 SHORT_12_KEN
N190 GOTOF END
;*********************************************************************************
N200 MIDDLE:
N210 MIDDLE_12_KEN
N220 GOTOF END
;*********************************************************************************
N221 MIDDLE_620:
N222 MIDDLE_12_620_KEN
N223 GOTOF END
;*********************************************************************************
N230 SHORT_AWD:
N240 SHORT_12_AWD_KEN
N250 GOTOF END
;*********************************************************************************
N260 LONG:
N270 DXX_12
;*********************************************************************************
N280 END:
N290 M30



In line N130, there is a variable “PARTNUMBER”, but I cannot figure out that how/where the machine builder define it. And how to transfer plc data to it?
Could you give me a help?

Thanks a lot.