The line coding format used in ISDN basic rate interface (BRI) at the S/T interface, which generally resides in a terminal adapter (TA). Pseudoquaternary coding is similar to alternate mark inversion (AMI) used in T1, with respect to the polarity of the framing bit and the requirement for bipolar violations (BPV) to compensate for long strings of zero (0) bits. The only difference is that pseudoquaternary coding has two levels of positive and negative voltage. See also AMI, BPV, BRI, framing bit, ISDN, Reference Point S, Reference Point T, and T1.