OSCCAL Value Finder Board with 16F88
The program loaded in the 12F675 device which has no osccal value will force a pulse on GPIO.4 and it will make a loop while increasing the osccal value internally. GPIO.5 will send the current osccal value used for each pulse sent. Because the device has no calibrated osccal value, the pulse will be variable. The circuit will wait until it receives the correct pulse. When the correct pulse is received, it will stop the test and display the osccal value used when the correct pulse was measured. The value displayed is in Hexadecimal format which means it can be used without conversions directly to the device?s memory.
Turning on the circuit, it will display the name of the project and then it will display the message ? Put Pic ? Hit But ?. At this point it?s possible to place the 12F675 device on the socket and press the push button. Pressing the push button S1 the circuit will start to measure the signal from the 12F675 device and will count the pulses. The display shows the pulse signal being measured and the current Osccal value. When the pulse sent by the 12F675 device matches the requested pulse length the circuit will stop the device and display the recommended osccal value. Since the circuit controls the power of the 12F675 device, at this point is possible to remove the device from the socket and place a new one. Pressing S1 the circuit will start a new test. This is a very interesting circuit for the microcontroller beginner. Not only for recovering lost osccal values but also to understand some microcontroller characteristics. The crystal must be a good quality crystal or precise results may not be ensured. The circuit uses an 8X2 LCD making it a portable project. visit page.