Scsi Cables - HP 9000 Series Service Manual

SCSI Cables

The information in this section is common to all types of SCSI busses.
1. The cable length used to connect the SCSI devices plus ANY cable length internal to the device
must not exceed the appropriate limits as previously stated.
2. Minimize the SCSI bus length but do not use cables shorter than 0.5m external.
3. Because cable impedance and construction affect bus signal quality, only HP cables are
recommended.
4. While the high-density SCSI connectors on the HP-PB Host Adapters support both thumbscrew
and squeeze latch cables, only the thumbscrew type are recommended because of reliability and
RFI concerns with the squeeze-latch cables.
Cable Characteristics
Single-Ended and Differential, 50 and 68 conductor flat cables or 25 and 34 single twisted pair cables
with a characteristic impedance of 90 to 140 ohms must be used for our application. (All Hewlett
Packard supplied cables meet this requirement.)
Voltages/Current
Single-Ended. Output Characteristics - Either open collector or tristate drivers.
Signal True (low) = 0.0 to 0.5 Vdc.
Signal False (high) = 2.25 to 5.25 Vdc.
Input Characteristics - Device powered on including drivers and passive receivers.
Signal True (low) = 0.0 to 0.8 Vdc.
Current = -0.4 to 0.0 mA @ 0.5 Vdc.
Signal False (high) = 2.0 to 5.25 Vdc.
Current = 0.0 to 0.1 mA @ 2.7 Vdc.
Differential. Output Characteristics:
V ol (Low-Level output voltage) = 1.7V max. at I ol (Low-Level output current) = 55 mA.
V oh (High-Level output voltage) = 2.7V min. at I hl (High-Level output current) = -55 mA.
V od (Differential output voltage) = 1.0V min. with common mode voltage ranges from -7 to +12
Vdc.
Input Characteristics:
I i (Input Current on either input) = +/- 2.0 mA. with input voltages between -7 and +12 Vdc. with
power on or off an with hysteresis = 35 mV min.
Chapter 11
SCSI Peripherals and I/O Information
11- 5