Basic function principles
The KL5001 terminal is an SSI interface for the direct connection of an SSI encoder. The terminal outputs a clock burst for reading the encoder and makes the incoming data stream available to the controller in the process image. Various operation modes, transfer frequencies, bit widths and code implementations can be selected. The individual configuration is permanently stored in a register set.
The LEDs indicate the operating state of the associated terminal channels.
- green Run LED:
- On: Normal operation
- Off: Watchdog-timer overflow has occurred. If no process data are transmitted by the Bus Coupler for 100 ms, the green LEDs go out.
SSI principles
SSI communication sequence
- The SSI master starts pulsing on the clock line with a fixed cycle into the shift register of the SSI slave.
- The slave generally "pushes back" data with a width of 25 bits on the data line. An SSI encoder should determine its position with the first falling edge of the signal at the Clock input ("latching"), which is then transferred.
- Once the specified number of bits was pushed, the clock signal is terminated.
- After a pause, polling by the SSI master recommences.
The last data bit can be a PowerFail bit, i.e. the slave signals a power failure. This output depends on the slave.
The number of bit changes equals the clock frequency, i.e. the maximum data transfer rate for a 1 MHz cycle is 1 Mbit/s.
Referencing an SSI signal
An SSI encoder is an absolute encoder, which means, that the position value is available without referencing immediately after switching on.
Many SSI encoders offer the option of referencing or zeroing the position value via an additional digital input. Depending on the signal voltage of the digital input on the encoder, this can be set, for example via a digital output terminal EL2xxx.
Alternative process data output format
The SSI interface is delivered with a data width of 24 bits and activated Gray binary conversion in the alternative output format. The baud rate to the SSI encoder is set to 250 kHz. The process data are output in the input data bytes D0 - D3. The mapping of the terminal in the alternative format is described in more detail in the chapter Terminal configuration.
Standard output format of the process data
4 bytes of input data are mapped in the bus coupler in the standard output format in the delivery state.