MC9S08JM16 Datasheet, PDF (207/386 Pages) Freescale Semiconductor, Inc – Microcontrollers

Initial conditions:
1) Clock supplied from ATE has 500 μs duty period
2) MCG configured for internal reference with 8MHz bus
START TRIM PROCEDURE
TRMVAL = $100
n=1
Multi-Purpose Clock Generator (S08MCGV1)
MEASURE
INCOMING CLOCK WIDTH
(COUNT = # OF BUS CLOCKS / 8)
COUNT < EXPECTED = 500
(RUNNING TOO SLOW)
CASE ST. ATEMENT ^{COUNT = EXPECTED = 500}
TRMVAL =
TRMVAL - 256/ (2**n)
(DECREASING TRMVAL
INCREASES THE FREQUENCY)
COUNT > EXPECTED = 500
(RUNNING TOO FAST)
TRMVAL =
TRMVAL + 256/ (2**n)
(INCREASING TRMVAL
DECREASES THE FREQUENCY)
STORE MCGTRM AND
FTRIM VALUES IN
NON-VOLATILE MEMORY
n = n+1
CONTINUE
YES
IS n > 9?
NO
Figure 12-13. Trim Procedure
In this particular case, the MCU has been attached to a PCB and the entire assembly is undergoing final
test with automated test equipment. A separate signal or message is provided to the MCU operating under
user provided software control. The MCU initiates a trim procedure as outlined in Figure 12-13 while the
tester supplies a precision reference signal.
If the intended bus frequency is near the maximum allowed for the device, it is recommended to trim using
a reference divider value (RDIV setting) of twice the final value. After the trim procedure is complete, the
reference divider can be restored. This will prevent accidental overshoot of the maximum clock frequency.
MC9S08JM16 Series Data Sheet, Rev. 2
Freescale Semiconductor
207