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AR# 24918

ML505/6 - IDT ICS843001-21 Fibre Channel Issue on ML505/6 boards


Keywords: fibre, fiber, channel, ML505, ML506, oscilliator, 25.5625 MHz, 26.5625 MHz, ICS843001-21

ML505/6 boards were built with an oscillator frequency value that does not support the Fibre Channel serial protocol. Oscillator X3 was inadvertently populated with a 25.5625 MHz oscillator instead of the correct value of 26.5625 MHz. This affects only Fibre Channel over the SFP or SMA MGT interfaces on the ML505/6 boards.

ML505/6 boards were built with an IDT Frequency Synthesizer IC, ICS843001-21, that is driven by three oscillators. A dipswitch 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. The IDT device, in turn, drives the MGT clock inputs on the Xilinx FPGA. Table 1-30 provided in the ML505/6 User Guide, UG347, provides more details on SW6 dipswitch 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 being used to derive Fibre Channel application frequencies. IDT has been contacted about the discrepancy in their data sheet. For more information about the operation of the ICS843001-21, please visit http://www.idt.com . The ICS843001-21 data sheet is available through their search engine.


Solution 1:
No action is required unless you require the use of Fibre Channel protocol on the ML505/6.

Solution 2:
Remove the half-sized, 8-pin DIP, 3.3V, 25.0 MHz socketed oscillator, X5, on the ML505/6, and replace it with 26.5625 MHz oscillator.

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 much more readily available as 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 X5, Cardinal P/N CPPFX C 4 L Z - A7-BR - 26.5625 TS.

Once you have replaced X5 on the ML505/6, you will have to use different dipswitch settings than those found in the board user guides. Please use the modified table below when selecting Fibre Channel frequencies from the ICS843001-21.

Updated Table 1-30 in ML505/6 UG347, where 57 = 26.5625 MHz (Socketed)

Updated Table 1-30 in ML505/6 UG347 Solution 2
Updated Table 1-30 in ML505/6 UG347 Solution 2

Solution 3:
Replace surface-mount parallel resonant crystal X3 with the correct frequency of 26.5625 MHz and use the table below. Abracon P/N ABLS-26.5625MHZ-B2F-T, a pin/package replacement, is available through distributors. Please visit the Abracon web page for a list of distributors in your area:
Abracon Data Sheet, ABLS-26.5625MHZ-B2F-T:

Updated Table 1-30 in ML505/6 UG347 Solution 3
Updated Table 1-30 in ML505/6 UG347 Solution 3

Reference Diagrams:
The Top side of the ML505/6 is shown below and highlights the locations of X3 and X5. The image was copied from the ML505/6 UG347.


AR# 24918
Date Created 09/04/2007
Last Updated 05/12/2008
Status Active
Type General Article