If you have a Scope (or access to one), you could do a simple test using a timing light to monitor timing, a scope to monitor voltage and frequency and a small wrench to create the knock / trigger the sensor. Its not perfect but will get you pretty close to finding out the info you want. With the engine running, if you tap on the block (somewhat close to the sensor with a 10mm wrench, you should be able to trigger the knock system to kick in and you'll see it with a timing light plus you'll possibly notice a ever so slight change in RPM due to the timing retarding. You should be able to see at what frequency the ECU's knock system kicks in and you should be able to see what happen's with the voltage by starting out with light taps and getting harder and harder untill you trigger the system...
There are other veriables that effect timing, but I dont know if they have any effect on knock control. One thing that many ECU's do (but Im not sure if the supra TCCS does this) is ignore / shut down the knock system above a certain RPM due to mechanical noise that can cause false knock sensor output.... This point is dependant on the engine design and the amout of mechanical noise it naturally produces at higher RPM's but most cause, but its usually above 5000 to 6000 RPM. Like for example, the MKII MR2's stop using knock sensor feedback above 6000RPM. Again, this is dependent on the engine.
Hope this helps...