Calibrating the internal 4mHz clock

[Mycroft2152]

There is an article in the recent isue of EDN Magazine about checking the calibration of the 4mHz clock on a PIC.

http://www.edn.com/article/CA6553623.html?spacedesc=designideas&industryid=44217&nid=2431&rid=1968712989


I'm not sure how it can be used on a PICAXE. but I'll leave it to the brain trust to figure it out.

Myc

 

[kranenborg]

If I get it right from the article the calibration factor for each individual new PIC is written to the last user memory byte. However, at program download all memory locations are cleared at the beginning, so it seems to me that this information is lost when a new PICAXE has arrived at the users desk ...

/Jurjen

 

[hippy]

The calibration value is held in Flash Memory, not user program memory ( Data Eeprom on the 08 through 20M ), so it remains intact during the lifetime of the PICAXE. Only certain PICmicro / PICAXE have such a calibration byte.

The calibration value can be read if you put the PICAXE in a PICmicro programmer, and in theory it should be possibly to alter it but I would not recommend trying it unless you are prepared to lose PICAXE functionality. It won't achieve much anyway, you can simply alter the OSCCAL value using POKE.

The PICAXE only needs to be recalibrated if erased or overwritten and that won't happen on a PICAXE unless something has gone badly wrong which would likely be accompanied by a small puff of smoke.

Such re-calibration only applies to using PICmicros not PICAXE's.

 

[Mycroft2152]

I was thinking more like comparing the 128 usec or 256 usec output of the 4060 to a equivalent output on a PICAXE. How would you get an ~128 usec output?

 

[hippy]

I'm not really sure how you mean on the comparison.

Generating 128us output ... PAUSEUS on the X1's/X2's, PULSOUT on the others, and for the 18X and others with a UART, send a $FF byte at the right baud rate so there's a single start-bit pulse of 128us ( although it would be active-low ).