Using the FS2331 DDR Probe with an Interposer (FS1024/25)
An interposer with the FS2331 is recommended if the user wants to see the activity in a specific DIMM slot or with a specific DIMM module. An interposer also provides the advantage of providing valid S0:3 signals to the FS2331, which makes it unnecessary to wire these signals from an adjacent DIMM slot in order to provide accurate Command decode on the FS2331 in those systems where S0:3 qualifies Command activity. The FS1024 and FS1025 interposers are the only interposers recommended for use with the FS2331. The user must be aware that the interposer provides additional trace length to the target system in a manner that the target is not designed for. This may have an impact on signal integrity or system operation.
When the FS2331 probe is used with an FS1024 or FS1025 DIMM interposer the chip select signals for the DIMM installed onto the interposer will automatically become visible to the probe. Most DIMMs will have only one or two ranks of memory, leaving two or three ports available on the probe to monitor the chip select signals for other DIMM slots.
When using an interposer with the FS2331 several jumper changes are needed.
1.Per the table on page 18, the jumpers for the signals S0:3 need to be changed.
2.A jumper needs to be removed from J9. This removes the 120 ohm terminating resistor from the CK0 input receiver on the FS2331 as it is now in parallel with the DIMM module.
DIMM Signal Loading Option
The FS2331 has the capability to add capacitive loading to all the signals on the DIMM bus. This capability may be of interest to users who want to emulate and measure a DIMM bus that may have many DIMM modules loading down Data and Command signals. This loading can be implemented using 0402 surface mount devices which can be soldered onto the FS2331 using existing surface mount pad locations around the top of the board. Please contact the factory for details on the layout of these locations. The FS2331 does not ship with any of these capacitors loaded.
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