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Nitron LCD Terminal

MON08 Programming and Debugging circuits

Nitron Oszillator trimming

AB32 Board

HC08 Flash programming

HCS08 Controller

HCS12 Controller

HC12 Welcome Kit


Zwobots Display






All Nitron MCUŽs have an internal oscillator, so they can run without an external clock. The internal oscillator runs at a 12,8 MHz, giving a busfrequency of 3,2 MHz. The internal frequency can vary by ± 25%. You can trim it to ± 0,4% of 3,2 MHz by writing the right value in the OSCTRIM register at adress $38. Normally the value from adress FFC0in FLASCH memory is copied into the OSCTRIM register. In Monitor Mode this happens automatically, in User Mode you must take care of this within your program. The problem is to get the right trim value for the oscillator. In Application Note AN2312 Motorola shows how this can be done. You can download the software at Motorola after registering. The application note describes two methods for callibration. Both methods need an external reference frequency. The first method uses a power line as reference clock. This is a little tricky to do, the other method is much easier. If you take a look at the schematics to send the reference frequency via RS232 you can see it is quite similar to the programming circuit.

You can use your programmer to calibrate the oscillator. Take care not to enter Monitor Mode. This can be done by not putting all the signals in the right state or removing the external oscillator. After you have done this, you can use Hyperterm to make a connection with 9600 Baud to the controller. Then send as many @ signs until the right value is found. If the right value is found the MCU signals this by toggeling PTA 3. You can check this by putting a LED to PTA3 or by checking the voltage at PTA3, which then should be ca. 2.5V.






   © 2005 by Eckhard Gosch •