Hi Alex,
The best way to generate PWM signals with a good time resolution in Simulink Real-Time is to use one of Speedgoat's configurable FPGA I/O modules together with an FPGA configuration file (bitstream) containing the PWM code module. The reason for that is the following: even if the switching frequency of your PWM signal is low, you need to sample it at a significantly higher rate to obtain a good timing resolution.
For example, if you have a PWM signal with a period of 20ms (which seems to be your use case) and want to obtain a duty cycle resolution of 1% or below, you need to sample your signal at least 100x faster, i.e. every 0.2ms (5kHz). In your specific case, 5kHz should be still be manageable to run on the CPU/model level to set/reset the digital output signal of your IO135 module every 0.2ms (for example using a "Pulse Generator" block), but the precision will be limited. If you are interested in sampling frequencies in the 50-100kHz range and above, your CPU will not be able to keep up with the sampling rate of the model and you will need to delegate the sampling of the PWM signal to a configurable FPGA I/O module.
I hope this is helpful!
Dimitri
