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1.4
Electrical Requirements
1.4.1
Single-Ended type
(1)
Termination circuit
All signals except for RESERVE, GND, or TERMPWR should be terminated at both ends of the
bus. Each signal should be terminated by one of the following methods. Figures 1.12 and 1.13
show the termination circuit.
a) Each signal must connect to the TERMPWR signal through 220 Ω (within ±5%) resistor, and
connect to ground through 330 Ω (within ±5%) resistor.
b) The termination circuit of each signal shall satisfy the following conditions.
1)
The terminators should be powered by the TERMPWR line. The circuit may receive
additional power from other sources but not require such additional power for proper
operation;
2)
Each terminator should source current to the signal line whenever its terminal voltage is
below 2.5 VDC and this current should not exceed 22.4 mA for any line voltage at or
above 0.5 VDC and 25.4 mA for any line voltage between 0.5 VDC and 0.2 VDC even
when all other signal lines are driven at 4.0 VDC;
3)
The voltage on all released signal lines should be at least 2.5 VDC;
4)
These conditions should be met with any conforming configuration of TARGs and INITs
as long as at least one SCSI device is supplying TERMPWR;
5)
The terminator at each end of the SCSI bus should add a maximum of 25 pF capacitance
to each signal;
6)
The terminator may not source current to the signal line whenever its terminal voltage is
above 3.24 VDC except terminators may source current when the voltage is above 3.24
VDC in applications where the bus is less than 0.3 m;
Figure 1.12 Single-Ended SCSI termination circuit-1
C141-C011
1-17
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