I see in the spec that you must use a 12, 16, or 24 Mhz crystal to use
USB. I'm currently using a 11.059Mhz. What happens if you don't?
Does it not produce a PLL Lock? Are there errors? Just curious. I
assume that I'm going to have to change my crystal to start using USB...
Sutton
USB PLL for LPC2148
Started by ●October 23, 2008
Reply by ●October 23, 20082008-10-23
-----Original Message-----
From: l... [mailto:l...]On Behalf
Of Sutton Mehaffey
Sent: Wednesday, October 22, 2008 9:23 PM
To: l...
Subject: [lpc2000] USB PLL for LPC2148
I see in the spec that you must use a 12, 16, or 24 Mhz crystal to use
USB. I'm currently using a 11.059Mhz. What happens if you don't?
Does it not produce a PLL Lock? Are there errors? Just curious. I
assume that I'm going to have to change my crystal to start using USB...
Sutton
Since USB is a serial protocol, I would imagine that this has to do with
getting the correct signaling rate. If I remember correctly, the frequency
is rather critical, which sometimes even prevents the use of ceramic
resonators.
I've always used 12 MHz, and USB works fine.
Mike
From: l... [mailto:l...]On Behalf
Of Sutton Mehaffey
Sent: Wednesday, October 22, 2008 9:23 PM
To: l...
Subject: [lpc2000] USB PLL for LPC2148
I see in the spec that you must use a 12, 16, or 24 Mhz crystal to use
USB. I'm currently using a 11.059Mhz. What happens if you don't?
Does it not produce a PLL Lock? Are there errors? Just curious. I
assume that I'm going to have to change my crystal to start using USB...
Sutton
Since USB is a serial protocol, I would imagine that this has to do with
getting the correct signaling rate. If I remember correctly, the frequency
is rather critical, which sometimes even prevents the use of ceramic
resonators.
I've always used 12 MHz, and USB works fine.
Mike
Reply by ●October 23, 20082008-10-23
On Thu, Oct 23, 2008 at 11:23 AM, Sutton Mehaffey wrote:
> I see in the spec that you must use a 12, 16, or 24 Mhz crystal to use
> USB. I'm currently using a 11.059Mhz. What happens if you don't?
> Does it not produce a PLL Lock? Are there errors? Just curious. I
> assume that I'm going to have to change my crystal to start using USB...
You would not be able to get 11.059MHz crystal to work.
http://www.beyondlogic.org/usbnutshell/usb2.htm#Electrical
Quote:
************************************
Another area which is often overlooked is the tolerance of the USB clocks.
This is specified in the USB specification, section 7.1.11.
* High speed data is clocked at 480.00Mb/s with a data signalling
tolerance of 500ppm.
* Full speed data is clocked at 12.000Mb/s with a data signalling
tolerance of 0.25% or 2,500ppm.
* Low speed data is clocked at 1.50Mb/s with a data signalling
tolerance of 1.5% or 15,000ppm.
This allows resonators to be used for low cost low speed devices,
but rules them out for full or high speed devices.
************************************
Or you can download the USB 2.0 specification from USB IF
website (http://www.usb.org).
Xiaofan
> I see in the spec that you must use a 12, 16, or 24 Mhz crystal to use
> USB. I'm currently using a 11.059Mhz. What happens if you don't?
> Does it not produce a PLL Lock? Are there errors? Just curious. I
> assume that I'm going to have to change my crystal to start using USB...
You would not be able to get 11.059MHz crystal to work.
http://www.beyondlogic.org/usbnutshell/usb2.htm#Electrical
Quote:
************************************
Another area which is often overlooked is the tolerance of the USB clocks.
This is specified in the USB specification, section 7.1.11.
* High speed data is clocked at 480.00Mb/s with a data signalling
tolerance of 500ppm.
* Full speed data is clocked at 12.000Mb/s with a data signalling
tolerance of 0.25% or 2,500ppm.
* Low speed data is clocked at 1.50Mb/s with a data signalling
tolerance of 1.5% or 15,000ppm.
This allows resonators to be used for low cost low speed devices,
but rules them out for full or high speed devices.
************************************
Or you can download the USB 2.0 specification from USB IF
website (http://www.usb.org).
Xiaofan
Reply by ●October 24, 20082008-10-24
Michael Anton wrote:
>
> -----Original Message-----
> From: lpc2000@yahoogroups .com
> [mailto:lpc2000@yahoogroups .com ]On
> Behalf
> Of Sutton Mehaffey
> Sent: Wednesday, October 22, 2008 9:23 PM
> To: lpc2000@yahoogroups .com
> Subject: [lpc2000] USB PLL for LPC2148
>
> I see in the spec that you must use a 12, 16, or 24 Mhz crystal to use
> USB. I'm currently using a 11.059Mhz. What happens if you don't?
> Does it not produce a PLL Lock? Are there errors? Just curious. I
> assume that I'm going to have to change my crystal to start using USB...
>
As far as I know, 48MHz is a magic number for USB. Those three clock
frequencies are evenly divisible into 48MHz. Disclaimer: I don't do USB
development, just some trivia I picked up along the way.
TomW
--
Tom Walsh - WN3L - Embedded Systems Consultant
http://openhardware.net http://cyberiansoftware.com http://openzipit.org
"Windows? No thanks, I have work to do..."
----------------
>
> -----Original Message-----
> From: lpc2000@yahoogroups .com
> [mailto:lpc2000@yahoogroups .com ]On
> Behalf
> Of Sutton Mehaffey
> Sent: Wednesday, October 22, 2008 9:23 PM
> To: lpc2000@yahoogroups .com
> Subject: [lpc2000] USB PLL for LPC2148
>
> I see in the spec that you must use a 12, 16, or 24 Mhz crystal to use
> USB. I'm currently using a 11.059Mhz. What happens if you don't?
> Does it not produce a PLL Lock? Are there errors? Just curious. I
> assume that I'm going to have to change my crystal to start using USB...
>
As far as I know, 48MHz is a magic number for USB. Those three clock
frequencies are evenly divisible into 48MHz. Disclaimer: I don't do USB
development, just some trivia I picked up along the way.
TomW
--
Tom Walsh - WN3L - Embedded Systems Consultant
http://openhardware.net http://cyberiansoftware.com http://openzipit.org
"Windows? No thanks, I have work to do..."
----------------
