DESCRIPTION
The DS21Q42 is an enhanced version of the DS21Q41B quad T1 framer. The DS21Q42 contains four framers that are configured and read through a common microprocessor-compatible parallel port. Each framer consists of a receive framer, receive elastic store, transmit formatter, and transmit elastic store. All four framers in the DS21Q42 are totally independent; they do not share a common framing synchronizer.

FEATURES
■ Four T1 DS1/ISDN-PRI/J1 framing transceivers
■ All four framers are fully independent
■ Each of the four framers contain dual twoframe elastic-store slip buffers that can connect to asynchronous backplanes up to 8.192MHz
■ 8-bit parallel control port that can be used directly on either multiplexed or nonmultiplexed buses (Intel or Motorola)
■ Programmable output clocks for Fractional T1
■ Fully independent transmit and receive functionality
■ Integral HDLC controller with 64-byte buffers configurable for FDL or DS0 operation
■ Generates and detects in-band loop codes from 1 to 8 bits in length including CSU loop codes
■ Pin compatible with DS21Q44 E1 enhanced quad E1 framer
■ 3.3V supply with 5V tolerant I/O; low-power CMOS
■ Available in 128-pin TQFP package
■ IEEE 1149.1 support