DS2125 データシートの表示（PDF） - Maxim Integrated

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DS2125

Ultra3 LVD/SE SCSI 15-Line Terminator

Maxim Integrated 

Figure 2. SCSI Bus Configuration

TERMPWR

TPWR

ISO

DS2125 Ultra3 LVD/SE SCSI 15-Line Terminator

CONTROL LINES (15)

TPWR

ISO

TERMPWR

VREF

DIFFSENS

DIFF_CAP

4.7µF

0.1µF

20kΩ

DIFFSENSE

20kΩ

DIFFSENS

DIFF_CAP

VREF

0.1µF

4.7µF

TPWR

ISO

VREF

DIFFSENS

DIFF_CAP

4.7µF

CONTROL LINES (15)

TPWR

ISO

DIFFSENS

DIFF_CAP

VREF

4.7µF

Note: The following terms are used throughout this data sheet:

DIFFSENS: Refers to the SCSI bus signal.

DIFFSENSE: Refers to the DS2125 pin name and internal circuitry capable of driving the DIFFSENS line.

DIFF_CAP: Refers to the DS2125 pin name and internal circuitry relating to monitoring the DIFFSENS line.

DETAILED DESCRIPTION

The DS2125 combines LVD and SE termination with DIFFSENSE sourcing and detection. A bandgap reference is

fed into two amplifiers, which creates a 1.25V reference voltage and a 2.85V reference voltage. The control logic

determines which of these references are applied to the termination resistors. If the SCSI bus is in LVD mode, the

1.25V reference is used. If the SCSI bus is in SE mode, the 2.85V reference is used. That same control logic

switches in/out parallel resistors to change the total termination resistance accordingly. Finally, in SE mode the Rp

pins are switched to ground.

The DIFFSENSE circuitry decodes trinary logic. There is one of three voltages on the SCSI control line called

DIFFSENS. Two comparators and a NAND gate determine if the voltage is below 0.6V, above 2.15V, or in

between, which indicates the mode of the bus as SE, HVD, or LVD, respectively.

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