Figure 15. Lvd Output Signals - Seagate ST39173N Product Manual

Barracuda 9LP Product Manual, Rev. C
9.7.2.2 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 "DIFFSENS" is betwen
+0.7 V and +1.9 V, the drive interface circuits operate low voltage differential and up to and including 40 M
transfers/s 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. Drives must
operate only in the mode for which the installation and interface cabling is designed. 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 X3T10/
1142D).
Multimode signals
Multimode circuit SE alternative signal characteristics are the same as described in Section 9.7.1. The SE
alternative for these circuits is selected as described above. SE cables and termination must be used.
Multimode circuit LVD alternative signal characteristics are not the same as the differential signals described in
Section 9.7.2.1. The SCA-2, 80-pin connector signal/pin assignments are the same for HVD and LVD (see
Tables 13c and 13e), 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 pro-
vided for by the Host equipment designers or end users.
The SE and differential alternatives are mutually exclusive.
Output characteristics
Each signal (V ) driven by LVD interface drivers shall have the following output characteristics when measured
s
at the disc drive connector:
Steady state Low level output voltage* = –.95 V = < V
Steady state High level output voltage* = –.95 V = < V
Differential voltage = +0.6 V minimum with common-mode voltage ranges 0.700 V = < V
*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.
LVD Differential
Driver
Signal +
Signal –
LVD Differential
Driver
Signal +
Signal –
|V | = .6V
0
Figure 15. LVD output signals
= < –1.55 V (signal negation/logic 0)
s
= < 1.55 V (signal assertion/logic 1)
s
1.55V –15ma
.95V +15ma
.95V +15ma
1.55V –15ma
cm
V = True / Logic 1 / Assertion
0
V = False / Logic 0 / Negation
0
71
= < 1.800 V.