The binary code can be processed very easily by computer systems. When using optical read-out, errors may occure, because the change from one bit to another on the different concentric tracks (LSB, LSB+ 1 ... ) is not exactly synchronized. Due to this, without any correction of the code, the position information could be wrong. 

The Gray Code is a single-step code. This indicates, that from one position to the next only 1 bit is changed. The reliability of the code detection is increased, which leads to a high position-reliability. 

The gray code is used to opticaly read out the position for all absolute encoders 

The extraction of a defined part of the gray code leads to the gray-excess code. This code enables the generation of non binary based divisions, e.g. 360, 720, 1000, 1440. 

The code values increase when the shaft is urning clockwise. lf the most significant bit (MSB) is inverted, the code values decrease when the shaft is turning clockwise 

To transfer the position data to a controller, different interfaces are available. 

This type of transfer is very fast. All bits of a position are transferred simultaneously each via a separate line. 

Compared to the parallel interface, the SSI interface needs less components and the EMC-characteristics are much better. In 

addition less cores are needed for trans­mission and the possible cable length is much longer. 

With the first shift of the clock signal from low to high CD the most significant bit (MSB) of the angular data is applied to the shaft encoder's serial output. With each succeeding rising edge, the next less significant bit is shifted to the data output. After transmission of the least significant bit (LSB) the Alarm bit or other special bits are transferred, depending on configuration. Then the data line switches to low CD until the time tm has passed. 

The number of clock pulses necessary for data transfer is independent of the reso­lution of the absolute shaft encoder. The clock signal can be interrupted at any point, or continued in ring-register mode for repeated polling. 

A further transfer of data cannot be started until the data line switches to high © again. lf the clock pulse sequence is not interrupted at point CD, the ring-register mode is activat­ed automatically. This means that the data stored at the first clock pulse transition CD are returned to the serial input si via the terminal so. As long as the clock pulse is not inter­rupted at CD, the data can be read out as often as wanted (multiple transfer).