All terminators independent of location shall be powered from the TERMPWR and TERMPWRB contact(s). The use of keyed connectors is recommended in SCSI devices that provide terminator power to prevent accidental grounding or the incorrect connection of terminator power.
( Regulatory agencies may require limiting maximum (short circuit) current to the terminator power lines. Recommended current limiting is 1,5 A for TERMPWR and 2 A for TERMPWRB. For systems utilizing multiple initiators, the initiators may be configured with option straps or current limiting devices. Maximum available current should not exceed 5 A. )
SCSI devices shall sink no more than 1,0 mA from TERMPWR and no more than 1,0 mA from TERMPWRB except to power an optional internal terminator.
Single-ended SCSI devices providing terminator power on cable A shall have the following characteristics: VTerm = 4,25 V d.c. to 5,25 V d.c. 900 mA minimum source drive capability
Differential SCSI devices providing terminator power on cable A shall have the following characteristics: VTerm = 4,0 V d.c. to 5,25 V d.c. 600 mA minimum source drive capability
Single-ended SCSI devices providing terminator power on cable B shall have the following characteristics: VTerm = 4,5 V d.c. to 5,25 V d.c. 1500 mA minimum source drive capability
Differential SCSI devices providing terminator power on cable B shall have the following characteristics: VTerm = 4,0 V d.c. to 5,25 V d.c. 1000 mA minimum source drive capability
( It is recommended that the terminator power lines be decoupled at each terminator with at least a 2,2 uF high-frequency capacitor to improve signal quality. )
Figure 9 - Alternative 1 termination for single-ended devices
Figure 10 - Alternative 2 termination for single-ended devices
Figure 11 - Termination for differential devices
Figure 12 - Differential driver protection circuit