Barracuda 18LP Family: ST39175LW/LC ST318275LW ... - Seagate

Barracuda 18LP Product Manual, Rev. E 65
9.7 Electrical description
“LC” models use the single connection attachment (SCA) connector. This 80-pin connector is designed to plug
directly into a back panel or plane. No external cables are required. Active terminators on the back panel must
be provided by the user. This connector is not recommended where cabling is required.
“LC” and “LW” models are Multimode drives. That is, their I/O circuits can operate as either single-ended or low
voltage differential drivers/receivers (selectable using the I/O “DIFFSENS” line). They require external terminators.
See Section 9.7.1 for additional information on these models.
See ANSI Standard T10/1302D for detailed electrical specifications.
9.7.1 Multimode—SE or LVD alternative
“LW” and “LC” models have I/O circuits that can operate either in single-ended (SE) or low voltage differential
mode (LVD). When the interface “DIFFSNS” line is between 0 V and .6 V, the drive interface circuits operate
single-ended and up to and including 20 M transfers/s (Fast-20 or Ultra-1 SCSI). When “DIFFSNS” is between
+0.7 V and +1.9 V, the drive interface circuits operate low voltage differential and up to and including 40 M
transfers/sec or less (Fast-40 or Ultra-2 SCSI). This arrangement is not intended to allow dynamically changing
transmission modes, but rather to prevent incompatible devices from attempting to interoperate. Multimode I/O
circuits used by “LC” and “LW” devices do not operate at high voltage differential levels and should never be
exposed to high voltage differential environments unless the common mode voltages in the environment are
controlled to safe levels for single-ended and low voltage differential devices (see the ANSI SPI-2 specification
T10/1302D).
Multimode signals
Multimode circuit SE alternative logic sense and signal level characteristics are described as follows:
Vil (low-level input voltage) = 1.0 V maximum (signal true); minimum = Vss – 0.5 V
Vih (high-level input voltage) = 1.9 V minimum (signal false); maximum = Vdd +0.5V
Vihys (Input Hysteresis) = 425 mV minimum
Multimode circuit LVD alternative signal characteristics are not the same as high voltage differential signals
(HVD). This drive does not support HVD. The SCA-2, 80-pin connector signal/pin assignments are shown in
Tables 13b and 13d, but the electrical characteristics of the signals are not the same. “LC” and “LW” model
drives do not have onboard terminators. The Multimode signal lines (either SE or LVD) should be terminated
with 110 ohm active terminator circuits at each end of the total cable. Termination of the I/O lines must be provided
for by the Host equipment designers or end users.
The SE and differential alternatives are mutually exclusive.
Output characteristics
Each LVD signal (V s ) driven by LVD interface drivers shall have the following output characteristics when measured
at the disc drive connector (refer to figure 12):
Steady state Low level output voltage* = –.95 V = < V s = < –1.55 V (signal negation/logic 0)
Steady state High level output voltage* = +.95 V = < V s = < 1.55 V (signal assertion/logic 1)
Differential voltage = +0.6 V minimum with common-mode voltage ranges 0.700 V = < V cm = < 1.800 V
A signal that is “released” goes to the negated (false or logic 0) state because the bias of the terminator pulls
the signal levels to the negated state.
*These voltages shall be measured between the output terminal and the SCSI device’s logic ground reference.
Refer to paragraphs 7.2.2, 8.3.2, and Annex A of ANSI SPI-3 specification, T10/1302D for details regarding
LVD circuits.
The output characteristics shall additionally conform to EIA RS-485.