This paper reports a half-rate bang-bang clock and data recovery (BBCDR) circuit supporting the trimodal (NRZ/PAM-4/PAM-8) operation. The observation of their crossover- points distribution at the transitions introduces the single-loop phase tracking technique. In addition, low-power techniques at both the architecture and circuit levels are employed to greatly improve the overall energy efficiency and multiply data throughput by increasing the number of levels on the magnitude. Fabricated in 28-nm CMOS, our BBCDR prototype scores a 0.29/0.17/0.14 pJ/bit efficiency at 14.4/28.8/43.2 Gb/s under NRZ/PAM-4/PAM-8 modes, respectively. The jitter is < 0.53 ps (integrated from 100 Hz to 1 GHz) with approximately-equivalent constant loop bandwidth, and we achieve at least 1-UI pp jitter tolerance up to 10 MHz for all the three modes.