8-bit MicrocontrollersのトピックRe: Internal oscillator tolerance after production

Internal oscillator tolerance after production

Hank — Fri, 12 Oct 2007 16:14:51 GMT

In the manual I found the following sentence: "The internal oscillator circuit is designed for use with no external components to provide a clock source with tolerance less than ±25% untrimmed. An 8-bit trimming register allows adjustment to a tolerance of less than ±5%.

Now my question:

Is the tolerance after production 25% or 5%, what means is the controller after production trimmed or untrimmed?

Re: Internal oscillator tolerance after production

Alban — Fri, 12 Oct 2007 16:28:52 GMT

Hello Hank,

Difficult to comment on a book without the reference
May be you should read this post: [IMPORTANT] Reminder of Rules to post on technical boards

You have to see if your provider if he/she is supplying trimmed MCUs or not.
You can also look at the trim address if the content is $FF or programmed.

When you mass erase the device, you also erase the trim value and have to reprogram it !

Cheers,
Alban.

Re: Internal oscillator tolerance after production

Ake — Fri, 12 Oct 2007 18:31:43 GMT

Hank,

I assume that you are looking into the MC68HC908QY4 book or something like it.

In that book it states what you have read.

The tolerance without any modified OSCTRIM register is 25%, which makes it oscillate at anything from 2.4 MHz to 4 MHz. Untrimmed the value of the OSCTRIM register is 0x80.

If the frequency is trimmed, the value will be maximum +/- 5% of, so the frequency will now be 3.04 MHz to 3.36 MHz.

The frequencies are the bus frequencies and are -40 C to + 125, VDD +/- 10%.

These figures are for the MC68HC908QY/QT.

Note: The OSCTRIM is not automatically loaded. You must take the value, from 0xffc0 and write it into the OSCTRIM register to make it have any effect.

Regards,

Ake