Siemens SINAMICS S120 Commissioning Manual page 424

Appendix
A.6 Overview of measuring systems / encoders
Absolute SSI protocol
Multiturn
1. Select in the drop-down list whether your encoder is multiturn-conform:
Singleturn resolution
Singleturn encoders divide one rotation (360 degrees mechanical) into a specific number of
encoder pulses, e.g. 8192. A unique code word is assigned to each position. After 360° the
position values are repeated.
1. Enter the singleturn resolution based on your encoder data sheet.
Multiturn resolution
Multiturn encoders also record the number of revolutions, in addition to the absolute position
within one revolution. To do this, further code disks which are coupled via gear steps with the
encoder shaft are scanned. When evaluating 12 additional tracks, this means that an
additional 4096 revolutions can be coded.
1. Enter the multiturn resolution based on your encoder data sheet.
SSI protocol structure
The SSI connection between the encoder and the encoder module is established using four
wires. This is a serial transmission.
The data transmission with the SSI protocol is performed in just one direction, i.e. the data
are transferred from the encoder to the evaluation module. The data is a position value for a
rotary or linear measuring system and, possibly, further bits that describe the position value.
The structure of the telegram differs depending on the encoder manufacturer and the
measuring system. Consequently, you must use the information provided by the
manufacturer that describes the protocol structure in detail. Manufacturers frequently extend
the position value and leading and trailing zero bits to produce a telegram length of 13, 21 or
25 bits. Whereby this information is extended to 9 bits for a telegram of 21 bits or to 12 bits
for a telegram of 25 bits. In the meantime, however, any telegram length is common. In the
following example, 29-bit position data are transferred and extended with 3 bits before and
after the position.
424
Commissioning with Startdrive
Commissioning Manual, 11/2017, 6SL3097-4AA10-0BP1