DS21T09
The DS21T09 consists of three major functional blocks, Figure 2:
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•
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Voltage reference, terminating resistors, and isolation switches
Bus current sensing circuitry
Bus ground sensing circuitry
When the Bus Ground Sensing Circuitry or Bus Current Sensing Circuitry determines that the SCSI bus
is properly terminated without the DS21T09, the power-down buffer isolates the resistors from the SCSI
bus and disables the power amp, thereby placing the DS21T09 in a low power mode (the bus sensing
circuitry always stays active). The
PDO
(Power-Down Output) pin can be connected to the pin of a
DS21T07 SCSI terminator for Wide SCSI configurations, Figure 8.
DS21T09 BLOCK DIAGRAM
Figure 2
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DALLAS [ DALLAS SEMICONDUCTOR ]
