Cable / Harness Testing
Communication Integrity Analysis

Do you need to test cables and cable harnesses? You will soon find out that simple continuity testing is not sufficient and that special attention has to be given to the high-speed signal nature of 1394 data transmission. And what can be better than real data streaming and simultaneous error analysis?

Even though FireSpys® are “general purpose” 1394 analyzers and on first sight seem a bit of overkill, certain features can be perfectly used for cable testing purposes. Many of our customers have already had invested in our analysis tool and now benefit from this additional functionality. Because of 1394 specifics a multi-channel tool is needed; configured as both data transmitting and receiving/verification devices the Triple FireSpys® (FS3810 or FS3850) provide just that functionality. Originally developed to analyze the triple redundant bus architecture of the F-35 program nearly all program members now also utilize the additional function. Please click here for further details on FireSpy® uses and GUIs for cable testing.

Granted that the classical analysis is done via Eye Diagram Testing. But these tests require a fairly expensive setup and the test cycles are long. Additionally, the cables are not tested with real data transmissions but with test signals representing the same frequency, signal levels, etc. Actual 1394 transmission analysis on the other hand either utilizes existing 1394 analyzers from DapTechnology or - if no equipment exists yet - gives a perfectly good justification for a purchase as it offers so many more testing possibilities for future requirements. It is not just a dedicated tool!

So what can be tested with a FireSpy®? FireSpy® bus analyzers offer PHY Register Query functionality and physical layer communication verification (CRC error analysis). Is the latter quantitative? If you need to know how many packets had a transmission errors then the answer is YES! Do you need the exact number of how many individual bits flipped then the answer is NO. CRC analysis does not give that level of detail. However, we really believe that running a full BERT is not always needed and semi-quantitative results as provided by the FireSpy can be satisfactory.

Levels of Communication Integrity Testing
Category Description Qualitative Quantitative Standard(s)
PHY Register Query

Read local and remote PHY registers

     Y     N     - /1394b
Physal Layer Communication Send Packets and verify CRCs      Y    (Y) 1394a/1394b
BER Testing Bit-by-bit Transmission verification      Y     Y 1394a/1394b

Setup Requirements

The easiest approach is to use the FireSpy® and the Adapter Cable to connect directly to the UUT. The UUT can be a single cable or a series of cables and devices. In this scenario the Adapter Cable connectors need to be matched to the UUT’s connectors.

There is one noteworthy limitation: Should the UUT be stretching the length limitation then the losses in the FireSpy® internal connector and the Adapter Cable (needs to be as short as possible) cannot be neglected and might affect performance and signal integrity.

In such a scenario (or when the UUT is physically further separated from the FireSpy®) DapTechnology recommends a solution with an additional repeater (2 channel). In such a setup the signal going into the UUT would be as close as possible to the real world’s signaling characteristics as the PHYs in the repeater will recondition the signal generated by the FireSpy®. DapTechnology offers repeaters that can be powered of a standard 12V AC/DC adapter or off the typical 28V aircraft power.

For obvious reasons the dual channel repeater can also be split in two single channel repeaters.

Frequently asked Questions:

Q: Can I simply connect the RX and TX pair on a single node and use such a loop-back for a cable test?

A: No! In 1394 this constitutes a loop and automatic loop-breaking mechanisms will resolve this non-allowed topology.

Q: How will the equipment "test" that the cable assembly is ok or not (e.g. what output/indications,etc.)?

A: The FireSpy® would run a cable test script within the Scriptor engine. Part of its functionality is to generate packets on one node, transmit them through the UUT, receive them on the other 1394 node and check for their correctness (CRC verification). Any bit flips during the transmission would result in an incorrect CRC and the FireSpy® would count these. At the end of the test (you define how many test packets you would send) the count can be compared to predefined values for pass/fail notifications in the script’s control panel.

Q: Would a repeater as described above effect the bus topology/node count?

A: Yes, it does. Each Physical layer chip will add to the node count. However, if the reference setup (FireSpy® - Repeaters - Self test cable) runs reliably without errors, then the additional nodes do not matter for a cable test. The key is that the repeaters basically create a "fresh signal" and the resulting data are a true representation of the cable performance.

Q: I was told that there was not (known anyway) a repeater that could be used in line with the Pulse TM1062TXHUA transceivers. Is this that true?

A: The issue here might be the term “repeater” as it is often misused. For DapTechnology and in the entire 1394 community a “repeater” is a device with essentially includes a 1394 PHY layer chip. In the aerospace world repeaters are normally built with active transformers in order to have balanced equalization, isolation, etc. So the above questions can be answered with NO, and these repeaters exist from DapTechnology… But: other people have used the term differently. If used just to refer to a device that simply reamplifies the signal then then the questions needs to be answered with YES. Such a device does not exist and will technically not work. You cannot just take an already deteriorated signal and amplify it again. This does not open up a closed eye again.