Cypress FM4 Series - Page 122

CHAPTER 2-3: High-Speed CR Trimming
122 FM4 Peripheral Manual, Doc. No. 002-04856 Rev. *E
Xtrm Calculation Procedure Example
Figure 4-5 shows an Xtrm calculation procedure example. Perform frequency trimming in the two stages
of coarse adjustment and fine adjustment.
Figure 4-5 Xtrm Calculation Procedure Example
Xtrm_coarse=
No
Yes
Xtrm_fine=
Yes
End
Calculate the coarse adjustment
(TRD[9:5]) bit (Xtrm_coarse)
Set an Xtrmmin_coarse value as the MCR_FTRM
(TRD=0b0000000000)
Base timer ch.0
PWC timer operation
Set a trigger for base timer on the rising of
the divided high-speed CR clock
Read TIMER1 value
Set an Xtrmmax_coarse value as the MCR_FTRM
(TRD=0b1111100000)
Base timer ch.0
PWC timer operation
Read TIMER2 value
Calculate Tmin_coarse and Tmax_coarse,
based on measured TIMER1 and TIMER2 values:
Tmin_coarse = (TIMER1×PCLK)/DIV
Tmax_coarse = (TIMER2×PCLK)/DIV
Calculate Xtrm_coarse (TRD set value at Ttgt):
{(Ttgt - (Tmax_coarse-Tmin_coarse) / 31-
Tmax_coarse} /{(Tmin_coarse-Tmax_coarse) / 31}
F
CRH
<= 4MHz ?
Set an Xtrm_coarse value as TRD[9:5]
Base timer ch.0
PWC timer operation
Read TIMER value
Set Xtrm_coarse - 1 as TRD[9:5]
Calculate the fine adjustment
(TRD[4:0]) bit (Xtrm_fine)
Set an Xtrm_coarse value as the MCR_FTRM
(TRD[9:5]=Xtrm_coarse)
Base timer ch.0
PWC timer operation
Read TIMER1 value
Set an Xtrmmax_fine value as the MCR_FTRM
(TRD[4:0]=0b11111)
Base timer ch.0
PWC timer operation
Read TIMER2 value
Calculate Tmin_fine and Tmax_fine,
based on measured TIMER1 and TIMER2 values:
Tmin_fine = (TIMER1×PCLK)/DIV
Tmax_fine = (TIMER2×PCLK)/DIV
Calculate Xtrm_fine (TRD set value at Ttgt):
{(Ttgt - (Tmax_fine-Tmin_fine) / 31-
Tmax_fine} /{(Tmin_fine-Tmax_fine) / 31}
Set an Xtrm_fine value as TRD[4:0]
Base timer ch.0
PWC timer operation
Read TIMER value
Set an Xtrmmin_fine value as the MCR_FTRM
(TRD[4:0]=0b00000)
4MHz <= F
CRH
<= 4.08MHz ?
Set F
CRH
< 4MHz : Xtrm_fine + 1 as TRD[4:0]
Set F
CRH
> 4.08MHz : Xtrm_fine - 1 as TRD[4:0]
No
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