mcf51ac256a Freescale Semiconductor, Inc, mcf51ac256a Datasheet - Page 398

• Manufacturer Part Number: mcf51ac256a
• Description: Mcf51ac Flexis
• Manufacturer: Freescale Semiconductor, Inc

Multipurpose Clock Generator (MCGV3)
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
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.
16-30
Initial conditions:
1) Clock supplied from ATE has 500 μsec duty period
2) MCG configured for internal reference with 8MHz bus
INCREASES THE FREQUENCY)
(DECREASING TRMVAL
TRMVAL - 256/ (2**n)
MCF51AC256 ColdFire Integrated Microcontroller Reference Manual, Rev. 5
COUNT < EXPECTED = 500
(RUNNING TOO SLOW)
TRMVAL =
n = n + 1
IS n > 9?
(COUNT = # OF BUS CLOCKS / 8)
DECREASES THE FREQUENCY)
Figure 16-13. Trim Procedure
NO
START TRIM PROCEDURE
INCOMING CLOCK WIDTH
(INCREASING TRMVAL
TRMVAL + 256/ (2**n)
TRMVAL = $100
CASE STATEMENT
TRMVAL =
MEASURE
YES
n=1
.
COUNT > EXPECTED = 500
(RUNNING TOO FAST)
COUNT = EXPECTED = 500
Figure 16-13
NON-VOLATILE MEMORY
STORE MCGTRM AND
Freescale Semiconductor
FTRIM VALUES IN
CONTINUE
while the