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AR# 24921

ML405 - IDT ICS843001-21 Fibre Channel Issue on ML405 boards


ML405 boards were built with an oscillator frequency value that does not support the Fibre Channel serial protocol. Oscillator X10 was inadvertently populated with a 25.5625 MHz oscillator instead of the correct value of 26.5625 MHz. This issue affects only Fibre Channel over the SFP or SMA MGT interfaces on the ML405 boards.

ML405 boards were built with an IDT Frequency Synthesizer IC, ICS843001-21, that is driven by three oscillators. A dip switch is used to control the selection of the three input oscillators, as well as the selection of the Multiply and Divide values available in the ICS843001-21 device. In turn, the IDT device drives the MGT clock inputs on the Xilinx FPGA. Table 19 in the "ML405 Evaluation Platform User Guide" (UG210) provides more details on SW14 dip switch settings.

One of the three oscillators driving the ICS843001-21 device has an incorrect frequency to support Fibre Channel serial protocol. A typographical error in the IDT data sheet resulted in the incorrect selection of a crystal frequency value of 25.5625 MHz to derive Fibre Channel application frequencies. IDT has been contacted about the discrepancy in their data sheet. For more information on the operation of the ICS843001-21, go to the following site and refer to the ICS843001-21 data sheet available through the IDT search engine:



Solution 1:

No action is required unless you require the use of the Fibre Channel protocol on the ML405.

Solution 2:

Remove the half-sized, 8-pin DIP, 3.3V, 25.0 MHz socketed oscillator, X7 on the ML405, and replace it with 26.5625 MHz.

Half-sized DIP oscillators can be purchased from a variety of sources, such as DigiKey, which carries crystal oscillators, as well as programmable oscillators. Programmable oscillators are more readily available because they are programmed and shipped to the end user. DigiKey carries programmable oscillators from Cardinal Components that are a drop-in replacement for socketed Oscillator, X7, Cardinal P/N CPPFX C 4 L Z - A7-BR - 26.5625 TS. See the following for more information:


Once you have replaced X7 on the ML405, you must use dip switch settings that are different from those listed in the board user guide. Use the modified table below when selecting Fibre Channel frequencies out of the ICS843001-21.

Updated Table 19 in ML405 UG210, where X7 = 26.5625MHz (Socketed)

Updated Table 1-30 in ML405 UG347 Solution 2
Updated Table 1-30 in ML405 UG347 Solution 2

Solution 3:

Replace surface-mount parallel resonant crystal X10 on the ML405, with the correct frequency of 26.5625 MHz and use the table below. Epson P/N FA36525.5625MH-C3 is a pin/package replacement and is available through distributors. See the Epson Web page for a list of distributors in your area:


Epson Data Sheet, FA36525.5625MH-C3 :


Updated Table 1-30 in ML405 UG347 Solution 3
Updated Table 1-30 in ML405 UG347 Solution 3

Reference Diagrams:

The back of the ML405 is shown below and the locations of X7 and X10 are highlighted. This image is copied from the ML405 User Guide (UG210).


AR# 24921
Date Created 09/04/2007
Last Updated 12/15/2012
Status Active
Type General Article