DESCRIPTION The DS21Q55 is a quad MCM device featuring independent transceivers that can be software configured for T1, E1, or J1 operation. Each is composed of a line interface unit (LIU), framer, HDLC controllers, and a TDM backplane interface, and is controlled via an 8-bit parallel port configured for Intel or Motorola bus operations. The DS21Q55 is software compatible with the DS2155 single transceiver. It is pin compatible with the DS21Qx5y family of products. ic.com Note: This Product Pre