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11.6.4
Electrical description
Model ST12400N uses single ended interface signals. These signals must be terminated with 110 ohm active
termination circuits at each end of the total cable. The terminators are enabled (or disabled) by installing (or
removing) jumper plug TE. See Figure 10.1-1. Single Ended circuits use open collector or three state drivers. See
Figure 11.6.4-1 and 11.6-1. The model ST12400NC uses single ended interface signals, but there are no provi-
sions for terminators on the drive.
The model ST12400ND 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 11.6.4-2 for circuit drawing. Differential I/O drives
are shipped without terminators. These drives have no provisions for adding terminators on the PCB. On these
drives some method of external termination must be provided by the user Systems Integrator or host equipment
manufacturer.
11.6.4.1
Single ended drivers/receivers
Typical single ended driver and receiver circuits for the ST12400N and ST12400NC are shown in Figure 11.6.4-
1. Terminator circuits shown (Note [1]) are to be enabled only when the disc drive is first or last in the daisy-chain.
See paragraph 11.6.4.3.
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.
Product Manual - Hawk 2 Family SCSI-2 (Volume 1), Rev. C
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