What is the maximum possible IMO accuracy of PSoC® 4 and why it is restricted to it?
The Internal Main Oscillator has an accuracy of +/- 2 percent. In PSoC devices, the WCO (32-kHz watch crystal oscillator) can be used to dynamically trim IMO to an accuracy of +/- 0.2 percent. The IMO block provides two hardware-controlled frequency TRIM registers for this purpose. The CLOCK_TRIM_1 register controls the IMO output in steps of 120 kHz and the CLOCK_TRIM_2 register provides a finer control of 15 kHz per step. As a result, the IMO trim accuracy is +/- 15 kHz. The +/- 15-kHz accuracy translates to about +/- 0.2 % for an 8 MHz IMO and improves for higher clock.