What is the difference between Unipolar and Bipolar mode operation?
Bipolar and unipolar modes are two different ways for an LIU to interface to a framer or back end ASIC. The following is from the receive perspective. The transmit perspective is similar. The T1 or E1 data (zeros and ones) is coded as alternate positive and negative pulses for signaling logic 1’s on the line. Zeros are coded as a zero voltage. In bipolar mode, two data lines, (RPOS and RNEG) plus a clock line (RCLK) connect the LIU to the framer. A logic “1” on RPOS tells the framer that a positive pulse was detected on the line. A logic “1” on RNEG tells the framer that a negative pulse was detected on the line. In bipolar mode, it’s the framer’s responsibility to decode the sequence of positive and negative pulses into a sequence of logic zeros and ones. This is done by the AMI or B8ZS/HDB3 decoders inside the framer. In unipolar mode, only one data line (RDATA) plus a clock (RCLK) connect the LIU to the framer. The sequence of positive and negative pulses is decoded inside the LIU.
