Cypress FM4 Series - Page 277

CHAPTER 7-2: VBAT Domain(A)
FM4 Peripheral Manual, Doc. No. 002-04856 Rev. *E 277
Not Linking with Clock Control Circuit
If always using the backup power supply to keep the RTC operating, do not link the 32 kHz oscillation
circuit with the clock control circuit.
The average power consumption of the entire system can be reduced by executing the following
operations: keep only the VBAT operating with the backup power supply, and use the hibernation control
of the VBAT Domain or the external circuit to turn off the VCC power supply while processes by the CPU
are not necessary.
 Example of setting procedure
(1) Set the Register of VBAT I/O Port to use the 32 kHz oscillation circuit.
(2) Set an appropriate current value for the current that is to flow to the oscillation amplifier circuit.
(3) Set the oscillation boost time.
(4) Disable the cooperative operation with the clock control circuit.
In addition, enable the oscillation.
 Examples of operation
32K_Init
(1) Write “01” to VBPFR[5:4].
End
(2) Write “Data” to CCB.
Write “Data” to CCS.
(3) Write “Data” to VB_CLKDIV.
Write “Data” to BOOST.
(4) Write “00” to WTOSCCNT[1:0].
VBAT
VCC
32kHz
Oscillation boost time