to:  Bill Spence, Chair, SPI WG
 
cc:  John B. Lohmeyer, X3T9.2 Chairman
 
dt:  May 15, 1992
 
fr:  Steve Hunley ........SAHX

re:  Proposed change to SPI
 
ref: fraft working document SCSI-3 Physical Interface
 
Mr. Chairman, I am proposing the following changes to the subject document as 
a result of conflicts I have discovererd while examining practical circuit 
design atlernatives for SCSI-3 I/O port applications.
 
Respectfully,
Steve Hunley, Texas Instruments, Inc.
P.O. Box 655303, Mail Stop 3655
Dallas, TX 75265
Tel: (214)997-2508
Fax: (214)997-5083
 
=================================================================
change from:
 
6.1.2 Single-Ended Input Characteristics
 
IIL (Low-level input current)  = -20 to 0 uA at Vi=0.5 volts dc
IIH (High-level input current) = 0 to 20 uA at Vi=2.7 volts dc
 
=================================================================
change to:
 
6.1.2 Single-Ended Input Characteristics
 
IIL (Low-level input current)  = -100 to 100 uA at Vi=0.5 volts dc
IIH (High-level input current) = -100 to 100 uA at Vi=2.7 volts dc
 
=================================================================
 
Discussion:
 
1)  I recommend to change the 0 uA limit in both the IIL and
    IIH specifications to account for parasitic pn junction leakages
    that will occur.
 
2)  I recommend to change both the 0 uA and 20 uA limits in both
    the IIL and IIH specifications to account for the inclusion of
    pull-up or pull-down current in the I/O port design that will
    bias the pin at a known logic state when the pin is in the
    open-circuit condition.
 
3)  To my knowledge, the above recommended changes will not compromise
    any other specification constraints embodied by the subject spec.