A test module is provided for testing system modules. All the test circuitry and test connectors reside on the test module. The test module is coupled to the system modules during testing, and is removed from the system after testing. Test connectors and test circuitry on the test module support such test functions as voltage margining, CPU emulation, and JTAG boundary scanning. A JTAG selection function can also be provided for selecting one or more JTAG loops for testing individually or as a single loop. The test module further includes level shifters for converting between 3.3V and 1.2V.
A midplane has plated through holes (PTHs) which form a first profile and a second profile. The first profile has (i) an overlapping portion which overlaps at least part of the second profile and (ii) a non-overlapping portion which does not overlap any part of the second profile. A first connector mounts to a first side of the midplane over the first profile, and a second connector mounts to a second side of the midplane over the second profile. At least one PTH is a shared PTH which resides in both the first and second profiles and which engages a pin of the first connector and a pin of the second connector. Additionally, at least one PTH is a non-shared PTH which resides in the non-overlapping portion of the first profile and which engages a pin of the first connector without engaging any pins of the second connector.
