Termination and 3.3 Volt Systems X3T10/94-164R1
Paul D. Aloisi 603-429-8687
aloisi at uicc.com
Fri Jul 22 14:11:20 PDT 1994
3.3 Volt Systems SCSI Termination X3T10/94-164R1
3.3 Volt SCSI Termpwr
3.3 Volts doesn't work with a diode drop.
3.3 Volts minus tolerance minus a diode drop is less
than 3.0 Volts.
3.3 Volt Systems will connect to 5 Volt systems
requiring a regulator for 3.0 to 5.25 Volt operation.
Unidirectional Circuit Breakers are required for less
than 0.2 Volt drop.
Section 7.3 Add a note Use a Unidirectional Circuit
Breaker instead of a diode and fuse for 3.3 Volt
Change SPI table 7 (Add a line) 3.3 Volt Single-ended
3,00 VDC Min, 5,25 VDC Max, 1500 mA
3.3 Volt Basics
3.3 Volt systems require terminators that will work down
to 3,0 VDC at the far end of the bus.
Note: Standard regulated terminators only work from
4,0 to 5,25 VDC.
Not all 3.3 Volt systems can provide current for the
terminator at the far end. example 32 bit PCMCIA adapters
have 1 Amp maximum available for the logic and termpwr.
3.3 Volt systems must work with termpwr provided from
a 5 Volt System.
Add Special ICONS in ANNEX H to show 3.3 Volt and Limited
termpwr current. (See Mailing for the proposed ICON.)
Termination with 3.3 Volt systems.
SCSI-2 Alternative has an Option for 2.7 Volt regulated
termination. This will allow a 0,3 Volt drop out regulator
to be used for the terminator with 110 ohm resistors meets
the SCSI-3 24 mA at 0.2 Volts.
Battery Systems will often require that termpwr is provided
for the far end termination. This could be either 3,3 Volt or
5,0 Volt systems.
All 3,3 Volt Terminators shall met all termination
requirements with Termpwr voltages from 3,0 to 5,25 VDC.
Add a line to section 7.1.1 3,3 Volt Systems terminators must
meet all specification with termpwr from 3,0 to 5,25 VDC.
Low Power Mode
Battery systems with short buses do not need standard
Buses with less than 0,3 meters length within an
enclosure can use reduce currents 1 mA typical.
Terminator must switch to normal termination currents
when an external cable is attached.
Signal line 50 on the 68 Pin connector or Singal line 22
on the 50 pin connector should be used to detect the
presents of an external cable.
Add an Informative Annex to describe the 3.3 Volt systems and
low/normal termination power modes.
More information about the T10