KL2521-xxxx - One Channel Pulse Train Output Terminals, RS422 / 24 V DC

Basic Function Principles


The KL2521 output terminal generates a binary signal with a variable frequency. The peripheral side of the electronics is electrically isolated from the internal K-bus, and therefore also from the fieldbus. The output frequency can be adjusted. 16-bit values (signed integer) can be provided for this adjustment through the controller's process image. These values modify the output frequency from zero up to a pre-selected maximum frequency in equal increments -> there are 32767 (15 bits) steps in each direction (right/left).

In contrast to the KL2521, on the KL2521-0010 terminal the two inputs +T and +Z are not available any more. Instead of that, the KL2521-0010 is equipped with additional outputs.
The outputs T and Z can be set via the CONTROL byte (CONTROL.4 and CONTROL.5).
Afterwards, the signals can be read back from the terminal. They will be displayed in the STATUS byte and transmitted directly to the PLC (STATUS.4 and STATUS.6).
The outputs are realized by MOSFET switches and can switch AC and DC voltages. The maximum current is 100 mA. DC voltages can be switched positive and negative.


Process image

In the delivery state the KL2521 terminal occupies 3 bytes in the process image. The mapping of the KL2521 can be set by means of the controller or by the Bus Coupler's configuration interface using the Beckhoff KS2000 configuration software.


Operation modes

In addition to the FM (frequency modulation) operation mode, the KL2521 can also be used to control stepper motors with pulse-direction control (frq. cnt pulse mode). Incremental encoder simulation is another operation mode. It is possible to connect the terminal output directly to an incremental encoder input, with which many servo drives and frequency converters are equipped.


Default setting

The KL2521 is set to FM mode by default, with a base frequency of 50 kHz and a resolution of 15 bits. The number of pulses output is read back into a 16 bit register.

The counter overflows with a signal to the controller. This is displayed by Status.3 (overflow) or Status.2 (underflow). In parallel with these two bits, Status.6 is set as a general error bit. This makes the extension to more than 16 bits easier for the control software to handle. The overflow can also be read from register 3 (internal 32-bit extension).

The counter can be cleared by Control.5. The clearing of the counter takes place

on a rising edge if Feature.4 = 1 (default)
This function is level-controlled if Feature.4 = 0.

If Bit Feature.10 = 1, Bit Control.5 sets the counter to a value specified by register R0 (low word) and register 1 (high word).



The base frequencies are specified with their resolution of 1 Hz per bit (GF1: registers 36, 37 or GF2: registers 38, 39). The terminal operates internally at 16 MHz with a resolution of 32 bits. This corresponds to a theoretical minimum step size of 0.0037 Hz/step over the entire frequency range. The output stage allows a maximum frequency of 500 kHz to be output

Additional information
Ramp function
Travel distance control
Output pattern