Product manual

60 Product Manual - Hawk 2 Family (Wide bus) SCSI-2 (Volume 1), Rev. A
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11.6.4 Electrical description
The ST12400W/WC models use single ended interface signals. These signals must be terminated with 110
ohm active termination circuits at each end of the total cable. ST12400WC drives have no provisions for
terminators on the PCB. On model ST12400WC some method of external termination must be provided by
the user, systems integrator or the host equipment manufacturer. On ST12400W drives terminator power
can be supplied from the drive to the I/O connector by the drive by properly positioning the TP jumper plug
and the J2 option select header. See Figure 10.1-1a. Single Ended circuits use open collector or three state
drivers. See Figure 11.6.4-1a and 11.6-1b.
The model ST12400WD uses differential interface signals and each of these must be terminated at each end
of the total cable with 330 ohms to +5 V and 330 ohms to ground with 150 ohms between each differential
pair. All I/O circuits are open collector, three state drivers. See Figure 11.6.4-1b for circuit drawing. ST12400WD
drives have no provisions for adding terminators on the PCB. Some method of external termination must be
provided (where needed) by the user, systems integrator or host equipment manufacturer. The ST12400WD
model drive can furnish terminator power to the SCSI I/O cable by properly positioning jumper plug TP. See
Figure 10.1-1a.
11.6.4.1 Single ended drivers/receivers
Typical single ended driver and receiver circuits for the ST12400W/WC is shown in Figure 11.6.4-1a. Termi-
nator circuits shown (Note [1]) are to be enabled ("W" model) or installed externally only when the disc drive
is first or last in the daisychain.
Transmitter characteristics
Single ended drives use an ANSI SCSI compatible open collector single ended driver. This driver is capable
of sinking a current of 48 mA with a low level output voltage of 0.4 volt.
Receiver characteristics
Single ended drives use an ANSI SCSI single ended receiver with hysteresis gate or equivalent as a line
receiver.