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I M - H S S I - D T E

High speed serial interface STD 3.0 dughterboard interface for TTL input and output serial lines

The IM-HSSI-DTE provides a high speed serial interface which follows the HSSI Design Specification Rev 3.0. This IM Module will provide a physical interface between the WAN Master card and high speed routers or other similar data devices such as fractional DS3. An electrical interface of this sort is necessary as the WAN Master can operate at speeds up to 20M Bits/sec on one channel. Other electrical interfaces such as RS-422 are limited to a maximum rate of 15M Bits/sec. More detailed Specifications are provided.

  • Operates at bit rates of up to 52 Mbps.
  • Compliant with HSSI Specifications Revision 3.0, April 12/93.
  • Gapped Clock feature gives flow control at high speeds
  • Expanded loopback signal protocol for testing
  • Supports loopback options. LA, LB and LC.
  • Compatible with the T1-Master and WAN Master communications cards.
  • 2M(6ft) cable provides DTE interface using SCSI-2 Male connector.

    Many new DCE devices such as routers, T3 Multiplexers and T1 Demultiplexers have started to use the HSSI interface. HSSI has several advantages over competing serial interfaces such as V.35 and EIA-530(EIA-422). It can operate at higher data rates, has superior flow control, amd additional loopback capability.

    EIA-530 is limited in maximum bit rate to about 10 Mbps over short distances, while V.35 may even be somewhat lower. The HSSI interface can operate up to 52 Mbits/sec. Using emitter coupled logic (ECL), current mode drivers limit voltage swings and lowers the affect of cable capacitance. Differential voltage swings are typically 0.85V, with a mazimum rise time of 2.3 ns. Differential current mode devices also eliminate the high peak switching currents which can cause grounding problems in other logic families.

    Gapped timing is not available to EIA-530 or V.35 interfaces and it is a feature which may be used as an advantage, by new software and hardware designs. Gapped timing allows the DCE device to control the flow of data coming from the DTE by stopping the clock. Most frequently this is used to stop data flow until buffer space is available. This approach is an effective solution to RTS/CTS latency problems which can appear at higher speeds in other interfaces.

    Loopback control support for LA, LB and LC is provided in the IM-HSSI-DTE board. LA and LB are asserted by the DTE (IM-HSSI-DTE), while LC is asserted by the DCE.

    The IM-HSSI-DTE uses the same form factor as other IM modules and can be used with either the T1-Master or WAN Master communications cards. This module is a high speed serial interface adaptor which follows the HSSI Design Specification Rev. 3.0. It provides a physical interface between the T1-Master or WAN master cards and high speed routers, satellite modems, T3 Multiplexers, T1 Demultiplexers and other devices.

    Cable Options

    A special cable and connector are needed for the HSSI interfaces because of the high speed signaling. The standard cable provided with the IM-HSSI-DTE is the CBL.IM-HSSI-DTE. It is designed to plug into the IM-HSSI-DTE module using a 26 pin high density male connector on one end and has a HSSI compliant male DTE connector on the other. The cable is 25 twisted pairs, 2M(6ft) long and has 110 impedance at 50 MHz. 2M is the HSSI recommended nominal length although the HSSI specifications allow for cables up to 15M(50ft). The HSSI cable is similar to the SCSI-2 cable, but it has a different impedance. It is not recommended to use the SCSI-2 cable for HSSI applications.

    Three cable options are available. This includes:

      This is a standard interface cable which allows the IM-HSSI-DTE to plug into a HSSI compliant DCE device. The cable is 2M(6ft) in length.

      This is a test cable for connecting two systems with IM- HSSI-DTE modules installed.

      This is another test cable for connecting two systems with IM-HSSI-DTE modules. It provides alternative clock modes.



    26 Pin High Density Male Connector 50 Pin SCSI-2 Male Connector Signal Name
    1 1,7,26 SG Signal Ground
    19 2 RT+ Receive Timing +
    11 3 CA+ DCE Available +
    2 4 RD+ Receive Data +
    21 5 LC+ Loopback Circuit C +
    13 6 ST+ Send Timing +
    23 8 TA+ DTE Available +
    15 9 TT+ Terminal Timing +
    8 10 LA+ Looback circuit A +
    25 11 SD+ Send Data +
    17 12 LB+ Looback Circuit B +
    4 13,32,38 SG Signal Ground
    5 19,44 SG Signal Ground
    6 24 TM+ Test Mode +
    10 25,50 SG Signal Ground
    20 27 RT- Receive Timing -
    12 28 CA- DCE Available -
    3 29 RD- Receive Data -
    22 30 LC- Loopback circuit C -
    14 31 ST- Send Timing -
    24 33 TA- DTE Available -
    16 34 TT- Terminal Timing -
    9 35 LA- Loopback circuit A -
    26 36 SD- Send Data-
    18 37 LB- Loopback circuit B -
    7 49 TM- Test Mode -

    Nominal length = 6 ft.
    50 Pin Connector = AMP part # 749111-4 plus AMP Shell # 749193-2 or equivalents
    26 Pin connector = Mode # 30-811-0 plus Shielded (metal ) DB15 hood.
    Cable pairing: Pair '+' signal with '-' signal of the same name.
    Cable Physical Specification attached.

    HD 26 Pin Male to Board A (E1 Removed) HD 26 Pin Male B to Board B (E1 Removed) Signal
    1 1 SG to SG
    10 10 SG to SG
    4 4 SG to SG
    5 5 SG to SG
    25 2 SD+ to RD+
    26 3 SD- to RD-
    2 25 RD+ to SD+
    3 26 RD- to SD-
    15,13 19 TT+ and ST+ to RT+
    16,14 20 TT- and ST- to RT-
    19 15,13 RT+ to TT+ and ST+
    20 16,14 RT- to TT- and ST-
    23 11 TA+ to CA+
    24 12 TA- to CA-
    11 23 CA+ to TA+
    12 24 CA- to TA-
    8 21 LA+ to LC+
    9 22 LA- to LC-
    21 8 LC+ to LA+
    22 9 LC- to LA-
    17 6 LB+ to TM+
    18 7 LB- to TM-
    6 17 TM+ to LB+
    7 18 TM- to LB-

  • Boards A and B must have IUSC pin TxC programmed as output and Tx clock source.
  • Boards A and B must have E1 removed.
  • Both boards must have IUSC pin RxC programmed as input and Rx clock source.
  • 26 Pin connector = Mode # 30-811-0 plus Shielded (metal ) DB15 hood.
  • Cable drain wire (shield) must be connected directly to the metal housing of the connector at both ends of the cable.

    The IM-HSSI-DTE will comply to FCC Part 15, subpart B for class A Digital Devices.

    A good application for the IM-HSSI-DTE module is to form a link between the WAN Master communications card and T3 network services. The Digital Link DL3100* T3 Access Multiplexer can be directly connected to the T3 network. A PCI based communications server can be connected to the DL3100 using the HSSI interface port, permitting fractional T3 data rates of up to 20 Mbps.


    *DL3100 and Digital Link are tradesmarks of Digital Link. 

    Specification subject to change without notice.