SPI-2 driver test conditions

RMoore at corp.adaptec.com RMoore at corp.adaptec.com
Fri Apr 26 05:58:00 PDT 1996


* From the SCSI Reflector, posted by:
* RMoore at corp.adaptec.com
*
Form: Memo
Text: (32 lines follow)
Following up my proposal at the Milpitas SPI-2 meeting:

I recalculated the test conditions under the new assumptions for terminator 
characteristics, i.e., Rt ranges from 100 to 110 ohms and Vb from 100 to 125 
mV.

I also added another limit as Bill Ham suggested to enforce asymmetric 
driver strengths, by limiting In to 11 mA.

The new test conditions I am proposing for Section 10.1.1, Table 10, are as 
follows. Replace the first condition:
	416 mV <= Va <= 706 mV
with:
	249 mV + 0.3 * |Vn| <= Va <= 706 mV

Replace the second condition:
	381 mV <= |Vn| <= 977 mV
with:
	255 mV + 0.3 * Va <= |Vn| <= 714 mV

Remove the third condition:
	-277 mV < |Va| - |Vn| < 181 mV
It turns out that this condition is not necessary because restricting the 
maximum In to 11 mA (or |Vn| <= 714 mV) keeps the voltage ratio at the 
receiver within the 4:1 we are looking for.

I'd like to point out that my derivation assumes current mode drivers. Are 
these test conditions valid for voltage mode? Unfortunately I haven't had a 
chance to study that question.

	Richard Moore
	Adaptec Irvine Technology Center
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