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The Model ST123 has been shipping for several years. It performs a pin-to-pin continuity and shorts test and what we call an integrity test that assures that SCSI signal pairs are connected to twisted pairs in the cable. The ST123 has an LED indication of faulty pins in the continuity test and of faulty pin pairs in the integrity test. We assume that the cable assembly is made with cable that meets the SCSI specifications for impedance, shielding, twisted pairs, etc. The ST123 has connectors for testing cables with 50-pin high density and 50-pin centronics type connectors as well as the 68-pin high density. We offer an adapter for testing of cables with one or two 68-pin VHDCI connectors. Other than plugging the ST123 into a power line, there is no set up required and a SCSI cable assembly can be tested in a few seconds.
The Model ST1000 Handheld SCSI Cable Tester is a “pass/fail” tester introduced in 2003. Like the Model ST123, this device makes continuity, shorts and integrity tests. However, with the battery operated Model ST1000, you need plug only one cable connector into the unit and a “loopback module” onto the connector on the far end of the cable. This means that installed cables do not have to be removed in order to test them. That makes it ideal for testing in the field.
In addition to continuity and integrity tests, when connected to a powered SCSI bus segment the ST1000 will display the presence or absence of TERMPWR, display the measured value of DIFFSENSE and display whether the bus is Single-Ended (SE), HVD or LVD.
Also, the ST1000 performs a twisted pair location test to determine that the critical REQ and ACK signals are not in the outside layer of the cable. The REQ and ACK signals determine SCSI timing and are quite susceptible to noise. Assuring that REQ and ACK are in the core or middle layer of the cable assures that they have the maximum amount of shielding from outside noise sources. The ST1000 then displays the suitability of the tested cable assembly for use in SE, HVD or LVD SCSI bus segments.
The ST1000 has a 68-pin high density connector and adapters are available for testing cables with VHDCI and/or 50-pin connectors.
A few words about the importance of the integrity test in the testing of SCSI cables: At the speed that SCSI operates, the cable is an rf transmission line. As with all rf transmission lines the impedance of the line is very important in order to minimize the amount of energy reflected from the receiving device back to the transmitting device. These reflections can cause many very hard to trouble shoot problems ranging from a system that refuses to boot to a fault that occurs very infrequently. It is extremely important that SCSI signal pairs are assigned to twisted pairs in the cable in order to maintain the impedance that the cable is designed to meet and to reduce crosstalk to a minimum. Passing the continuity and integrity tests of Paralan SCSI Cable Testers assures that the cable assembly is not the source of problems in your SCSI system.
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