SCSI Interface - Electrical Specifications


SCSI Interface - Electrical Interface
These are the specifications as listed in ANSI X3.131-1986 for single ended SCSI operation.
See > SCSI-Bus Termination (Mixing SCSI types)

Output Signals 
All signals use open-collector or three-state drivers. Each signal driven by a SCSI device has the following output characteristics when measured at the SCSI device's connector :

   Signal   Definition                 Characteristics
   V OL     Low-level output voltage   0.0 to 0.5 volt DC at 48 mA sinking
                                       (signal assertion)
   V OH     High-level output voltage  2.5 to 5.25 volt DC (signal negation)

Input Signals 
SCSI inputs meet the following electrical characteristics on each signal, including both receivers and passive drivers:

   Signal   Definition                 Characteristics
   V IL     Low-level input voltage    0.0 to 0.8 volts DC (signal true)
   V IH     High-level input voltage   2.0 to 5.25 volts DC (signal false)
   I IL     Low-level input current   -0.4 to 0.0 mA at V=0.5 volts DC
   I IH     High-level input current   0.0 to 0.1 mA at V=2.7 volts DC

Minimum input hysteresis = 0.2 volts DC.
Maximum input capacitance = 25 pF (measured at the device connector closest to the stub, if any, within the device).


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