Stepper motor controller output is not really designed for such purpose. I can't guarantee that it will work but you can try the following:
1) STEPSPEED to define 600 pps in a single step
2) STEPMOVE to generate approximately 600Hz
3) using a 0.05s clock pulse to trigger a custom function and increase the output speed by 30 pps. You need a variable to keep track of that. When the output speed reaches 1200Hz, stop incrementing the speed. 10 seconds later, reverse the above steps.
Unfortunately the maximum pps generated by the stepper controller in T100M+ is only a "wish" and not necessarily accurate. If you need to be able to generate the frequency accurately and you are currently residing in US or Canada, pls write to support@tri-plc.com to inquire about the availability of the F2424 PLC which can generate very accurate stepper output frequency and it should work for this application.