Categorising Connectors

Connectors can only be fully tested if something is plugged into them. Therefore, unless they are being tested in that way, accessible connectors should be categorised as Ignored. This categorisation informs XJDeveloper that the connector will not drive any nets, and it is therefore safe for Connection Test to exercise nets on the connector to check for shorts and stuck-at faults.

To categorise connectors as Ignored, select them and click the Ignored tile. When prompted to add a note, it is advisable to provide a comment to explain why it is dealt with in this way (e.g. Nothing connected during testing). Such comments can be helpful for anyone reviewing the project at a later stage.

When a connector is tested by looping back between its own pins using a cable or a simple passive PCB, it's simplest to categorise the connector as Passive and to create a *.pdd file to define the links being made. Refer to Creating a New Passive Device Description File for guidance.

When a loopback links two different connectors, the connections should be defined in the Connections screen instead.

When it's tested by connecting a board that does more than just provide a passive loopback, details of that board can be provided on the Boards screen (defining it as a Test Fixture Board if appropriate), with the inter-board connections entered on the Connections screen.

In cases where loopbacks are defined in the Connections screen, you do not need to categorise the connectors involved because the connectors will automatically be moved to the Ignored category. They will be marked as [Connection device] in the Categorise Devices screen.

• When three non-adjacent pins on a connector have both read and write access, it's best to link them together for testing to improve open circuit analysis (but see the warning below). A loopback between only two pins allows an open circuit to be detected but does not allow the faulty pin to be identified. However, when three pins with read and write access are connected together, the fault's location can be found.

• When designing loopbacks to test a connector, it's important to ensure that joining connector pins together won't stop the system detecting shorts. For example, a loopback between physically adjacent pins would prevent a short between those same pins being detected. It is therefore advisable to avoid placing loopbacks between adjacent pins or between pins on nets that come close to each other anywhere on the PCB (e.g. pins 1 and 5 on a connector may appear suitable for linking together, but that would not be true if they connect to adjacent pins on the JTAG device).
• When choosing which pins to connect together, remember that you need read and write access to the joined net, preferably from different places. Therefore, you should not link a pin that only has read access to others with only read access; nor link one that only has write access to others with only write access.