MPC5553/MPC5554 Microcontroller Reference Manual, Rev. 5
11-30
Freescale Semiconductor
This routine will correct for process variations, but as temperature can change after the calibration has been
performed, variation due to temperature drift is not eliminated. This frequency modulation calibration
system is also voltage dependent, so if supply changes after the sequence takes place, error incurred will
not be corrected. The calibration system reuses the two counters in the lock detect circuit, the reference
and feedback counters. The reference counter is still clocked by the reference clock, but the feedback
counter is clocked by the ICO clock.
When the calibration routine is initiated by writing to the DEPTH bits, the CALPASS status bit is
immediately set and the CALDONE status bit is immediately cleared.
When calibration is induced, the ICO is given time to settle. Then both the feedback and reference counters
start counting. Full ICO clock cycles are counted by the feedback counter during this time to give the initial
center frequency count. When the reference counter has counted to the programmed number of reference
count cycles, the input to the feedback counter is disabled and the result is placed in the COUNT0 register.
The calibration system then enables modulation at programmed
Fm. The ICO is given time to settle. Both
counters are reset and restarted. The feedback counter begins to count full ICO clock cycles again to obtain
the delta-frequency count. When the reference counter has counted to the new programmed number of
reference count cycles, the feedback counter is stopped again.
The delta-frequency count minus the center frequency count (COUNT0) results in a delta count
proportional to the reference current into the modulation D/A. That delta count is subtracted from the
expected value given in the EXP field of the FMPLL_SYNCR resulting in an error count. The sign of this
error count determines the direction taken by the calibration D/A to update the calibration current. After
obtaining the error count for the present iteration, both counters are cleared. The stored count of COUNT0
is preserved while a new feedback count is obtained, and the process to determine the error count is
repeated. The calibration system repeats this process eight times, once for each bit of the calibration D/A.
After the last decision is made, the CALDONE bit of the SYNSR is written to a 1. If an error occurs during
the calibration routine, then CALPASS is immediately written to a 0. If the routine completed successfully
then CALPASS remains a 1.
shows a block diagram of the calibration circuitry and its associated registers.
shows a flow chart showing the steps taken by the calibration circuit.
6-8
480
9-14
320
15-20
240
21-31
160
Table 11-11. Multiplied Factor Dividers with M Values (Continued)
MFD
M
Summary of Contents for MPC5553
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