60 Product Manual - Hawk 2LP Family (Wide) SCSI-2 (Volume 1), Rev. A
_____________________________________________________________________________________
11.6.4.2
Differential drivers/receivers
Differential drivers and receivers are used by the "WD" and "DC" models. Typical circuits are shown in Figure
11.6.4-2. The drive has no provisions for terminator circuits on differential I/O drives.
Differential Signals
All differential interface signals consist of two lines dSIGNAL and -SIGNAL. A signal is true when
+SIGNAL is more positive than -SIGNAL, and a signal is false when -SIGNAL is more positive than +SIGNAL.
All assigned signals shall be terminated at each end of the cable as shown in Figure 11.6.4-2. Drive user or
systems integrator must provide some external means of termination.
Output Characteristics
Each signal driven by differential interface drives shall have the following output characteristics when
measured at the disc drive SCSI connector:
Low-level output voltage* = 2.0 V maximum at Low-level output current = 55 milliamps.
High-level output voltage* = 3.0 V minimum at High-level output current = -55 milliamps
Differential voltage = 1.0 V minimum with common-mode voltage ranges from -7 V dc to +12 V dc.
* These voltages shall be measured between the output terminal and the SCSI device’s logic ground reference.
The output characteristics shall additionally conform to EIA RS-485-1983.
Input Characteristics
Each signal received by differential interface drives shall have the following input characteristics when
measured at the disc drive SCSI connector:
Input current on either input = +2.0 milliamps maximum (includes both receivers and passive drivers).
This requirement shall be met with the input voltage varying between -7 V dc and +12 V dc, with power on or
off, and with the hysteresis equaling 35 mv, minimum.
The input characteristics shall additionally conform to EIA RS-485-1983.
