Callibrate WDT?

[j@qmail.com]

<font face="Courier New" size=-1>I need to know how long my pic16f876 program sleeps. Apparently, watch dog timers vary quite a bit:

setup_wdt(144ms); //
sleep(); // actually slept for 170ms.

I can do one chip with my scope, but how can I do many chips? The only thing I can think of is to set-up a second chip as a "sleep timer".

In other words, put a calibration program in the first chip to communicate with the sleep timer, and then save the results in eeprom for later use by the main application.

Any other methods?

Tnx,
Jay</font>
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This message was ported from CCS's old forum
Original Post ID: 14341

[Sherpa Doug]

:=<font face="Courier New" size=-1>I need to know how long my pic16f876 program sleeps. Apparently, watch dog timers vary quite a bit:
:=
:=setup_wdt(144ms); //
:=sleep(); // actually slept for 170ms.
:=
:=I can do one chip with my scope, but how can I do many chips? The only thing I can think of is to set-up a second chip as a "sleep timer".
:=
:=In other words, put a calibration program in the first chip to communicate with the sleep timer, and then save the results in eeprom for later use by the main application.
:=
:=Any other methods?
:=
:=Tnx,
:=Jay</font>

Beware the WDT may drift considerably with temperature or voltage changes. It is meant to be very reliable, but not very stable.

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This message was ported from CCS's old forum
Original Post ID: 14363

[Steve H.]

The WDT timer specifications are in the data sheets and they show that the WDT is not well controlled. In fact the article listed below is a link to an app note that shows how to use the WDT to measure temperature!
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This message was ported from CCS's old forum
Original Post ID: 14373

[Steve H.]

In the past I have also used a simple serial connection to talk to the flash chips during calibration of various things. I make a serial connection, calculate the various constants required and store the cal constants in the Flash EEPROM. Then the program is written to read those values upon startup forever more (or until the next cal).

This could take care of ther initial offset, but probably not the temperature and voltage drift.

Steve H.
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This message was ported from CCS's old forum
Original Post ID: 14374

[j@qmail.com]

:=:=<font face="Courier New" size=-1>I need to know how long my pic16f876 program sleeps. Apparently, watch dog timers vary quite a bit:
:=:=
:=:=setup_wdt(144ms); //
:=:=sleep(); // actually slept for 170ms.
:=:=

Thanks for the help folks! I am going to rethink my approach.

Jay
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This message was ported from CCS's old forum
Original Post ID: 14377