TITLE
    25-Pin SCSI Terminator: How To Build
Article ID:
Created:
Modified: 		3559
3/22/89
4/25/00
TOPIC

    This article contains information for constructing a 25-pin terminator

DISCUSSION

    Pinouts for the SCSI port are as follows:
    Pin No.
    Signal Name
    Description
    1
    REQ/
    Request
    2
    MSG/
    Message
    3
    I/O/
    Input/Output
    4
    RESET/
    Reset
    5
    ACK/
    Acknowledge
    6
    BSY/
    Busy
    7
    GROUND
    Signal Ground
    8
    DB0/
    Data Bit 0
    9
    GROUND
    Signal Ground
    10
    DB3/
    Data Bit 3
    11
    DB5/
    Data Bit 5
    12
    DB6/
    Data Bit 6
    13
    DB7/
    Data Bit 7
    14
    GROUND
    Signal Ground
    15
    C/D/
    Control/Data
    16
    GROUND
    Signal Ground
    17
    ATN/
    Attention
    18
    GROUND
    Signal Ground
    19
    SEL/
    Select
    20
    DBP/
    Data Parity
    21
    DB1/
    Data Bit 1
    22
    DB2/
    Data Bit 2
    23
    DB4/
    Data Bit 4
    24
    GROUND
    Signal Ground
    25
    TERMPWR
    +5 volts

    Inside the Apple SCSI Terminator each signal line (ends with "/") is connected to TERMPWR through a 220-ohm resistor and is also connected to GROUND through a 330-ohm resistor.

    TERMPWR           DB1/ (example)         GROUND

    |                    |                    |

    |                    |                    |

    |                    |                    |

    |                    |                    |

    |-----/\/\/\/\/------|-----/\/\/\/\/------|

    |      220-ohm       |      330-ohm       |

    |      resistor      |      resistor      |

    |                    |                    |

    |                    |                    |

    The obvious tradeoff here is cost versus time to build this terminator. It would seem that size is also an issue; this is a lot of resistors and solder joints to deal with.

    However, if someone needs it, and appearance is not an issue and energy is in abundance, this is a solution.

Document Information
Product Area: Computers; Peripherals
Category: Cables
Sub Category: SCSI
Keywords:

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