Simulating a custom discrete-time PI controller and plant in SIMULINK

Hi!

I've been looking to simulate a PI controller in SIMULINK without much success. You will be able to find a description of the above in the images located here: https://picasaweb.google.com/102197309611185157885/PIControlWithMatlabAndSIMULINK?authkey=Gv1sRgCOCnzvbm5PuNJA&feat=directlink.

I was able to use some of the SIMULINK supplied blocks to get started in simulating a PID(z) controller attached to a similar model of a DC motor with the feedback of dtheta (angular velocity in rad/s) passed to a zero-order-hold block. The input I used a speed reference (in rad/s again). I want to, however, replace the SIMULINK supplied block with a custom PI controller - see below:

Another approach would be to consider the freq. domain analysis of this model by considering the system's transfer function. This approach is taken here: http://www.library.cmu.edu/ctms/ctms/examples/motor/digital.htm However, it seems they are far more interested in the system stability-analysis. Is this the only approach?

Any suggestions would be appreciated.

Thanks, Mike.