X3T9.2/88-161

     LASER MAGNETIC STORAGE                            MEMO
     INTERNATIONAL
_________________________________________________________________________

                                                       6 December 1988

     To:       Members of X3T9.2

     From:     Paul Boulay
               (719) 593-4323

     Subject:  Single Ended Terminator Requirements 


The objective of this proposal is to identify the technical requirements 
to be met by alternative termination designs. If this change is made to 
the standard, use of terminators other than the traditional 220/330 ohm 
terminator will be allowed. This is desirable because a terminator with a 
lower characteristic impedance will provide a better match to currently 
available cables. 

The following text is proposed as a replacement for the text that defines 
the 220/330 terminator for a single ended SCSI bus.

All signals not defined as RESERVED, GROUND or TERMPWR shall be terminated 
at both ends of the cable as follows:

(1) The termination of each signal consists of 220 ohms to the TERMPWR 
line and 330 ohms to ground;

OR,

(2) The termination of each signal shall meet these requirements:

   (a) The terminators shall each supply a characteristic impedance 
between 100 and 132 ohms. 

(b) The terminators shall be powered by the TERMPWR line and may receive 
additional power from other sources but shall not require such additional 
power for proper operation. (The TERMPWR line is required to supply up to 
800 mA at between 4.25 and 5.25 V.)

(c) The current available to any signal line driver shall not exceed 48 mA 
when the driver asserts the line and pulls it to 0.5 V. Only 44.8 mA of 
this current shall be availably from the two terminators.

(d) The voltage on all released signal lines shall be at least 2.5 V when 
the TERMPWR line is at least 4.25 V. 

(e) These condidions shall be met with any legal configuration of targets 
and initiators as long as at least one initiator is supplying TERMPWR.