In chapter 54.2.3 VREF Trim Register 4 on page 1371 of MKL28ZRM rev.4 page 1371, VREF 2.1V is enabled when VREF2V1_EN bit is cleared, I think there must be a mistake here.
I already tested VREF module. It is is enabled when VREF2V1_EN bit is set and disabled when VREF2V1_EN is cleared. Thank you for your feedback, I will notify the appropiate area about this.
