soldering crystal oscillators

Former Member over 13 years ago

Several people have found that problems with usb and ethernet

were related to the 25MHz crystal oscillator. Perhaps this part

isn't always soldered correctly. One important recommendation is

that you "stand on the board while soldering".

http://cfm.citizen.co.jp/english/product/cvo_manual.html

see paragraph 1.II.2.

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YT2095 over 13 years ago

although I`m not quite familiar with ethernet, I have done a little work with USB, and that likes divisons or multiples of 12Mhz, that are taken care of on chip by either a divider or PLL.
25MHz seems a strange number to start with (as opposed to a 24MHz for instance), could that be causing the problems?
or can someone tell me how the 12MHz is derived for the USB please.

Thanks
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johnbeetem over 13 years ago in reply to YT2095

YT2095 wrote:

although I`m not quite familiar with ethernet, I have done a little work with USB, and that likes divisons or multiples of 12Mhz, that are taken care of on chip by either a divider or PLL.
25MHz seems a strange number to start with (as opposed to a 24MHz for instance), could that be causing the problems?
or can someone tell me how the 12MHz is derived for the USB please.
25 MHz is what the LAN9512 data sheet specifies for the XI/XO pins. They probably quadruple this internally to 100 MHz for 100 Mb/s Ethernet. For USB 2.0 you need 480 Mb/s so they probably need 480 MHz internally. They probably have a 480 MHz PLL oscillator divided by 96 to get a 5 MHz feedback signal. This is locked to the 25 MHz crystal reference divided by 5.
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Former Member over 13 years ago in reply to johnbeetem

Apparently the timebase for 100 Mbps ethernet is actually 125 MHz.
With 100BASE-TX hardware, the raw bits (4 bits wide clocked at 25 MHz at the MII) go through 4B5B binary encoding to generate a series of 0 and 1 symbols clocked at 125 MHz symbol rate.
-from http://en.wikipedia.org/wiki/Fast_Ethernet
See also: http://www.designspark.com/content/raspberry-pi-waveforms
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Former Member over 13 years ago in reply to johnbeetem

Apparently the timebase for 100 Mbps ethernet is actually 125 MHz.
With 100BASE-TX hardware, the raw bits (4 bits wide clocked at 25 MHz at the MII) go through 4B5B binary encoding to generate a series of 0 and 1 symbols clocked at 125 MHz symbol rate.
-from http://en.wikipedia.org/wiki/Fast_Ethernet
See also: http://www.designspark.com/content/raspberry-pi-waveforms
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