Ingo, 1. I think you will find that 50ppm means +/- 50ppm. 2. You may find that the 50ppm includes everthing! So you are clear on = this I will explain. There are basically three reasons why your xtal = frequency is not exactly where it should be: (a)Tolerance [manufacturing differences if you like] (b)Tempco [how the frequency varies over temperature] (c)Ageing [longe term changes in frequency] You may find that the 50ppm you need includes all of the above (or maybe = not)? If it does then you need to know all of the above. These are = always given on a basic xtal specification. Bog standard HC49 xtals will = do tolerance of typically +/- 30ppm with temp stability of +/-50 ppm, = ageing will be +/- 3ppm in year one and dropping off approx 50% of this = each year after. These basic xtals are probably not good enough for your = job. However, you can get tighter tolerance and tempco down to +/- 5ppm = which is much more than you need! Finally, rememgber that you need to = know what your operating temperature range is in order to fully spec = your xtal. Have a look at CMAC, GOLLEDGE, EUROQUARTZ sites to find out more STEVE =20 Steve Rogers B.Eng (Hons) C.Eng IEE RF Design Engineer Micromill Electronics Limited Leydene House Waterberry Drive=20 Waterlooville Hampshire PO7 7XX Tel: +44 (0) 23 9236 6600 Fax: +44 (0) 23 9236 6673 Registered No. 1456922 (England). =20 Registered Office Brook Road Wimborne, Dorset BH21 2BJ *********************************************************************** "This email and any attached files are confidential and may be legally = privileged.If you are not the addressee, any disclosure, = reproduction,copying, distribution,, or other dissemination or use of = this communication is strictly prohibited. If you have received this = transmission in error please notify the sender immediately and then = delete this email. It is the policy of Micromill Electronics Limited that no legally = binding statements, representations or commitments (collectively = 'statements') may be made by email. Any such statements must be = confirmed either by facsimilie or by post before they will have legal = effect. The sender of this email is not authorised to commit the company = in any way and the addressee is hereby formally notified of that fact." *********************************************************************** -----Original Message----- From: ingo.kupper@xxxxxxxxxxxxxx [mailto:ingo.kupper@xxxxxxxxxxxxxx] Sent: Monday, March 08, 2004 11:22 PM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] PPM Content-Type: text/plain; charset=3D"iso-8859-1" Content-Transfer-Encoding: quoted-printable Hi There, =3D20 I am designing an LOM (LAN on motherboard) and wonder about the =3D oscillator requirement in the data sheet. It says: "... driven by an external 25MHz crystal of 50PPM or better..." Now, I have seen data sheets saying =3DB150ppm or 50ppm - is that the = =3D same? I think, that 50ppm could actually mean =3DB125PPM - which is getting more precision for a higher purchase price. =3D20 Any opinion or real definition appreciated! =3D20 Thanks, =3D20 Ingo =3D20 =3D20 -- Binary/unsupported file stripped by Ecartis -- -- Type: image/jpeg -- File: Notebook.jpg ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.org List archives are viewable at: =20 //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu =20 ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email=20 ______________________________________________________________________ ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.org List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu