Is there a "standard" crystal value for AT91SAM7S designs?
It seems that the boot program would expect something specific for proper configuration of the PLL, serial, and USB devices. However, I can't find any guidance in the documentation.
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If you use an 18.432 Mhz crystal, then the USB can be used to flash the part at production. If you use anything else, then the USB will not work, but the UART will.
-- Best Regards, Ulf Samuelsson This is intended to be my personal opinion which may, or may bot be shared by my employer Atmel Nordic AB
part
Thanks, Ulf.
The 18.432/48 ratio seems a bit wide for this PLL -- divide by 48, multiply by 125? This works OK with this part?
Download one of the USB examples...
-- Best Regards, Ulf Samuelsson This is intended to be my personal opinion which may, or may bot be shared by my employer Atmel Nordic AB
If I use a 18.432 MHz crystal, then what values do I use for the caps and resistors connected to PLLRC?
The datasheet contains very little information, but hints that there is a "tool" available to calculate the values. I searched Atmel's website, and all I could find was an Excel spreadsheet application. I downloaded it, and selected the part I am using, AT91SAM7256. The first inputs it asked for was the "Input Divider Ratio" and the "Loop Divider Ratio" with no explaination for what these numbers mean, or what criteria I should use to select them. Furthermore, it appears to be impossible to use the spreadsheet to select any values that result in an output frequency lower than 88MHz. Yet, according to the datasheet, the max frequency for the chip is 55MHz.
The next number it asks for is the "PLL Frequency Bandwidth", with no explaination of what that means. The phrase "PLL Frequency Bandwidth" occurs nowhere in the 519 page datasheet. If I Google for "PLL Frequency Bandwidth" I get only one hit, for a non-relevant webpage on a server in Argentina.
Sorry if I sound a little frustrated.
-bob
Why not use a 20Mhz xtal instead of a 18.432Mhz one?
18.432Mhz divided by 5 and multiplied by 26 gives 95.846MHz, whereas 20MHz divided by 5 multiplied by 24 gives exactly 96MHz, a better value for USBIs it just because 18.432xtals are cheaper than 20Mhz ones?
ted
18.432MHz divided by 48, multiplied by 125 gives 48MHz.
However, this would drive 384 KHz into the PLL, which is lower than the 1MHz specified minimum in the datasheet.
BUT, the minimum output of the PLL is 80MHz and the data sheet talks about the PLL generating a 48MHz clock in quite a few places.. so I'm wondering if the PLL is a little wider than is specified.
Download the schematics from the atmel web page. Cut Paste Done ;-)
-- Best Regards, Ulf Samuelsson This is intended to be my personal opinion which may, or may bot be shared by my employer Atmel Nordic AB > > Sorry if I sound a little frustrated. > > -bob >
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No, because the BootROM assumes 18,432 Mhz. The SAM-BA USB flashing wont work without it, and you have to use the UART.
-- Best Regards, Ulf Samuelsson This is intended to be my personal opinion which may, or may bot be shared by my employer Atmel Nordic AB
Hi Ulf, Can you please provide a URL? I went to
Thanks,
-bob
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