The DS21455 and DS21458 are quad monolithic devices 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 DS21455* is a direct replacement for the older DS21Q55 quad MCM device. The DS21458, in a smaller package (17mm CSBGA) and featuring an improved controller interface, is software compatible with the older DS21Q55.