The primary function of the JTAG External Modules (JEM) for the DIMM/SODIMM Socket Cluster Test is to provide test access to off-board signals that otherwise could not be accessed by a JTAG test system and to strengthen the memory-independent JTAG testing for the assembly correctness of the following socket types:

• DIMM (Dual In-line Memory Module), miniDIMM, microDIMM, VLP DIMM sockets
• SODIMM (Small Outline Dual In-line Memory Module) sockets
• SORDIMM (Small Outline Registered Dual In-line Memory Module) sockets
• SOCDIMM (Small Outline Clocked Dual In-line Memory Module) sockets
• VLP SORDIMM (Very Low Profile Small Outline Registered Dual In-line Memory Module) sockets
• FBDIMM (Fully Buffered Dual In-line Memory Module) sockets
• etc.

For many designs, JTAG test has adequate access to on-board signals, but signals that go off the board often cannot be tested. By adding JTAG access to memory socket off-board signals, a JEM_DIMM/SODIMM module can increase the board's fault coverage, possibly reducing the need for developing alternative tests to reach the required test coverage level. The JEM_DIMM/SODIMM module provides a number of JTAG accessible individually controlled test channels that can be used to control and observe signals that go off the board.

The JEM_DIMM/SODIMM modules provide full bi-directional JTAG controllability and observability for all socket pins and is fully compatible with the following JTAG ATPG platforms:

Flynn Systems onTAP Series 4000
Corelis ScanExpress
JTAG Technologies ProVision
Asset ScanWorks

The ATPG tools of each of these JTAG test platforms can generate tests with the advanced diagnostics for the socket pins failure detection, as well as sensing analog voltages on the individual power pins (such as Vdd, Vddq, Vddspd and Vref). The JEM_DIMM/SODIMM module TAP channel can be combined with the board TAP chains or used as a separate TAP.