ifm electronic RM3001 - Handbuch (Seite 52)

52
3.3 Data exchange
3.3.1 Position
The input data of the encoder are only required for the position value with a defined length of 32 bits. As
an option the encoder supports a position value length of 16 bits. The value is right-justified in the data
field.
DDLM_Data - Exchange mode
Standard configuration:
Octet: 1 2 3 4
Bit 31 - 24 23 - 16 15 - 8 7 - 0
Data 2
31
- 2
24
2
23
- 2
16
2
15
- 2
8
2
7
- 2
0
data exchange - 32 bits
Configuration data:
- Device class 1:
D1hex 2 input data words, data consistency
- Device class 2: F1hex 2 input data words, 2 output data words
for preset value, data consistency
Optional configuration:
Octet: 1 2
Bit 15 - 8 7 - 0
Data 2
15
- 2
8
2
7
- 2
0
Data_Exchange - 16 bits
Configuration data:
- Device class 1:
D0hex 1 input data word, data consistency
- Device class 2: F0hex 1 input data word, 1 output data word for preset value,
data consistency
3.3.2 Preset value function
The preset value function enables the adaptation of the zero point of the encoder to the mechanical zero
point of the system. The preset value function sets the actual value of the encoder as preset value. The
preset value is stored in the encoder as output value when the Data_Exchange function is activated. The
preset value function is used after the scaling function. This means that the preset value is entered in the
current measuring unit.
The most significant bit (MSB) of the preset value controls the preset value function as follows:
Normal operating mode: MSB = 0 (bit 31, optionally bit 15)
The encoder will not change the preset value.
Preset mode: MSB = 1 (bit 31, optionally bit 15)
With MSB = 1 the encoder accepts the transferred value (bit 0 - 30) as preset value in binary code. The
encoder reads the current position value and calculates an offset value on the basis of the preset value
and the read position value. The position value is shifted by the calculated offset value. If the output
position value equals the preset value, the preset mode is terminated and the MSB can be set to 0 by the
master. The resulting offset value can be read by means of the diagnostic function. In case of voltage
breakdown, it is permanently stored in the encoder and is reloaded at each start-up.