Recalibration Utility Oscillator

Posted on Oct 15, 2012

The PIC 12F629 and 12F675 devices have an internal 4Mhz oscillator that enables the devices to be used without an external crystal or RC network. This frees up one or two pins for I/O use and allows the device to be built into minimum component count designs. The internal oscillator needs to be calibrated and this is achieved by reading a factory programmed calibration setting and writing it into the OSCCAL register during initialisation of the device by the application software.

The calibration word is located at the last address in the user program memory area, address 0x3FF. It is in the form of a RETLW instruction and the user code should include a CALL 0x3FF instruction which will return with the calibration setting in the

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