E10 doesn't have a first scan bit, but you can use the following emulation:
R1 T1
|---|/|--------(TIM)
|
| T1 R2
|---| |-------[DIFU]
[DIFU]
R1 and R2 are two internal relays. T1 is the timer.
R2 will therefore only trigger for one scan time only after T1 times out and you can use it for homing purpose. T1 can be 0.2 second so that the first scan is trigger 0.2s after the PLC has been powered ON.