What is the MAX Fcpu for ST7

y_gudekar · ‎2006-11-02

Posted on November 02, 2006 at 09:45

y_gudekar · ‎2006-10-11

Posted on October 11, 2006 at 09:15

Hello,

Currently I am using ST72F561 with a crystal of 9.8 MHz to get

accurate baudrates.

If the PLL is disabled. Fcpu is => (9.8 MHz) / 2.

When I Enable the PLL. Fcpu becomes => (9.8 MHz) * 2.

But now, even a simple code to toggle a port pin does not work.

Is there any Maximum ''Fcpu'' frequency for ST7?? If yes what is it??

Regards,

Amit

pete3 · ‎2006-10-11

Posted on October 11, 2006 at 09:52

8MHz core is the fastest you will get. This is on the datasheet pp21, 22 and 222.

You will notice core function is not guaranteed above this speed (hence your problem).

The fact the ST demo boards all use a 16MHz oscillator is not coincidence!

pete3 · ‎2006-10-11

Posted on October 11, 2006 at 09:53

PS Also make sure your option bytes are set correctly i.e. no PLL if this would take you over the max speed and check crystal frequency matches.

wolfgang2399 · ‎2006-10-11

Posted on October 12, 2006 at 05:50

.. in addition: please mind chapter 12.5.4 PLL Characteristics were they define the restricted (!) PLL input frequency range from 2 to 4 MHz.

Regards WoRo

emmanuel23 · ‎2006-11-02

Posted on November 02, 2006 at 09:45

Just one precision about the maximum possible speed of ST7 MCUs: even if 8MHz is the most common value for ST7 MCUs, keep in mind it depends on sales types.

For example the high speed usb microcontroller ST7268x can work up to a 30 MHz fcpu.

Besides, for some MCUs, it may depend on the supply voltage.

Anyway, for other people who would like to know the limit for a given salestype, the best way is to refer in the datasheet of the salestype (as peterwrigley did before answering the initial question...)