HEIDENHAIN PROFINET - Manual (Page 73)

Functional description of the encoder
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7.7 Preset value
The preset value function enables adaptation of the position value
from the encoder to a known mechanical reference point of the
system. The preset function sets the actual position of the encod-
er to zero (= default value) or to the selected preset value. The
preset function is controlled by bits in the control word (G1_STW)
and acknowledged by a bit in the status word (G1_ZSW). A preset
value can be set more than once and it can be stored to the non-
volatile memory using PROFIdrive parameter 971.
The preset function has an absolute and a relative operating mode
selectable by bit 11 in the Control word (G1_STW). Bit 11 and bit
12 in the Control word controls the preset in the following way.
Normal operating mode: Bit 12 = 0
In this mode, the encoder will make no change in the output val-
ue.
Preset mode absolute: Bit 11 =0, Bit 12 = 1
In this mode, the encoder reads the current position value and
calculates an internal offset value from the preset value and the
current position value. The position value is then shifted with the
calculated offset value to get a position value equal to the preset
value. No preset will be made if a negative preset value is used
while trying to initiate an absolute preset.
Preset mode relative: Bit 11 =1, Bit 12 = 1
In this mode the position value is shifted by the preset value,
which could be a negative or a positive value set by encoder pa-
rameter 65000 or 65002.
The steps below should be followed by the IO-controller when
modifying the Preset value parameters:
1. Read the requested Preset value parameter and check if the
returned value meets the application requirements. If not,
proceed with the following steps.
2. Write the Preset value into the individual parameter.
3. Store the value in the non-volatile memory by PROFIdrive pa-
rameter 971 if the value should be valid also after the next
power on sequence.
Note: The preset function should only be used at encoder
standstill.
Note: The number of possible preset cycles is unlimited.