Fast(20)-SCSI Single-ended drivers

[Kevin Gingerich]

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Application message id:  TI.msg.159139
Grade of Delivery:  Normal

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  To  SCSI Reflector   X400
 
>From  Kevin Gingerich  GING
 
Subj  Fast(20)-SCSI Single-ended drivers
 
Since most of the test results presented by Bill Ham for single-ended
Fast(20)-SCSI use the SN75LBC968, I thought the following information would be
helpful in deciding the final limits for specification. The min's and max.'s
are from SPI and not necessarily the achievable bounds.
 
The driver;
    Parameter                    Condition           Min.   Typ.  Max.  Unit
VOH, High-level output voltage   IOH= -20 mA         2.0    2.5          V
                                 IOH= -75 mA                2            V
                                 IOH= -90 mA                0.2          V
VOL, Low-level output voltage    IOL=  48 mA                0.25  0.5    V
                                 IOL= 100 mA                0.5          V
tr, 10-90% rise time             SPI circuit,15 pF    5     10          ns
                                 SPI circuit,100 pF   5     12          ns
tf, 90-10% fall time             SPI circuit,15 pF    5     10          ns
                                 SPI circuit,100 pF   5     12          ns
 
The receiver;
VIT+, Positive-going input threshold voltage                1.6    2     V
VIT-, Negative-going input threshold voltage         0.8    1.1          V
Vhys, Input hysteresis voltage (VIT+ - VIT-)                0.5          V
tw(n), Noise rejection pulse width                           5          ns
 
I will be unable to attend the WG meeting tomorrow and am recommending the
following to make the single-ended bus (as defined in the last meeting) work
more often than not. (If you want it to work all of the time use differential!)
The basis for the numbers is that the bus looks like about 25 ohms to the
driver in the middle of a fully loaded bus.
 
    Parameter                    Condition           Min      Max.   Unit
VOH, High-level output voltage   IOH= -32 mA          2               V
                                 IOH=   0 mA                  3.24    V
VOL, Low-level output voltage    IOL=  96 mA                  0.8     V
tr, 10-90% rise time             SPI circuit,15 pF    5              ns
tf, 90-10% fall time             SPI circuit,15 pF    5              ns
VIT+, Positive-going input threshold voltage                  1.8     V
VIT-, Negative-going input threshold voltage          1               V
Vhys, Input hysteresis voltage                       0.3              V
 
I do have some analyses to back these numbers and can present them at a future
date if needed.
 
Good luck in Milpitas,
Kevin Gingerich
Texas Instruments, Inc.
(214)997-3378
4307725 at mcimail.com