L DB2.DBW 0 // Read RHO4 counter
L "DB conveyor advance".Counter_memo // Read memorised counter
-I // DELTA = Counter - Previous counter
T "DB conveyor advance".Computed_gap //

L DB2.DBW 0 // Update memorised counter from RHO4
T "DB conveyor advance".Counter_memo //

L "DB conveyor advance".Computed_gap
L -500 // Test overlapping of counter
<I // in forward motion
JCN LBL1

L "DB conveyor advance".Computed_gap
L 1000 // DELTA correction modulo overlap
+I
T "DB conveyor advance".Computed_gap


LBL1: L "DB conveyor advance".Computed_gap // Test overlapping of counter
L 500 // in backward motion
>I
JCN LBL2

L "DB conveyor advance".Computed_gap
L 1000 // DELTA corection modulo overlap
-I
T "DB conveyor advance".Computed_gap

LBL2: L "DB conveyor advance".Computed_gap // Write DELTA into o/p word
T "DB conveyor advance".mm_Gap_on_PLC_cycle



为什么 "DB conveyor advance".Computed_gap 小于-500要加1000，而大于500减1000呢？有什么特殊用途吗？可以将500改成其它数值吗？