Can't find the value of tTOUT in the datasheet...

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Hmmm... just curious:
I looked in the datasheet (of mega8)...
Well... I just can't find the value for tTOUT [?!?] It seems important as this interval of time is to be added to those 16-17 ms of watchdog timeout.
So, IMHO, doggy-resetting the uC will take in fact (much) longer!

Real men don't use backups, they post their stuff on a public ftp server and let the rest of the world make copies.

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Quote:

It seems important as this interval of time is to be added to those 16-17 ms of watchdog timeout.

You lost me on that one. I suspect that tTOUT is, in fact, the watchdog interval.

Lee

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Ah, now it makes more sense. That's sthe clock startup time. Better info is given in Mega88 datasheet. >>You<< are the one to select that time, :) , and minimum is 0--but that may not be appropriate for your clock source.

Quote:
Clock Startup Sequence Any clock source needs a sufficient VCC to start oscillating and a minimum number of
oscillating cycles before it can be considered stable.
To ensure sufficient VCC, the device issues an internal reset with a time-out delay (tTOUT)
after the device reset is released by all other reset sources. “System Control and Reset”
on page 40 describes the start conditions for the internal reset. The delay (tTOUT) is
timed from the Watchdog Oscillator and the number of cycles in the delay is set by the
SUTx and CKSELx fuse bits. The selectable delays are shown in Table 5. The frequency
of the Watchdog Osci l l a tor i s voltage dependent as shown i n
“ATmega48/88/168 Typical Characteristics – Preliminary Data” on page 298.
Main purpose of the delay is to keep the AVR in reset until it is supplied with minimum
VCC.

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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This tTOUT is present for all the reset types:
- power-on reset;
- external reset;
- BOD reset;
- watchdog reset.

Real men don't use backups, they post their stuff on a public ftp server and let the rest of the world make copies.

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Don't you select the startup time with fuse (SUT0, SUT1) selections?

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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ka7ehk wrote:
Don't you select the startup time with fuse (SUT0, SUT1) selections?

Well Jim... I'm always enable the BOD; I think this is better than relying on the startup time (which is kinda blind as it checks nothing).

Real men don't use backups, they post their stuff on a public ftp server and let the rest of the world make copies.

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That is apples and oranges (mixing BOD & SUT). As the Mega88 datasheet says, the tTOUT is selected by >>your<< fuse settings.

Lee

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Now I have SUT1,SUT0 = 11.
So, Lee... you're saying that I should set:
SUT = 01 if I use BOD for my mega8 ?
... 'cause I don't wanna drop out the BOD.
I find BOD very useful, at least for the device I'm currently developing.
I think that running an AVR without BOD is like riding a bike without saddle. :roll:

Real men don't use backups, they post their stuff on a public ftp server and let the rest of the world make copies.

Last Edited: Tue. Dec 13, 2005 - 07:06 AM
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IMHO, that's not what he is saying. The selection of BOD and the SUT bits (startup time) are two completely different items. They can be selected to be whatever you want. However, the Atmega8 data sheet suggests using values for SUT10 of 01 when the BOD is selected.

Randy

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Quote:
the Atmega8 data sheet suggests using values for SUT10 of 01 when the BOD is selected.

Right, that's what I was saying!
Ok, it sounds like a confirmation to me. :wink:

Real men don't use backups, they post their stuff on a public ftp server and let the rest of the world make copies.

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OK, but it sounded to me that you were saying to Lee that choosing SUT=01 would not turn on the BOD. Sorry for the confusion!

Randy