Rainbow Electronics W90P710CDG User Manual
Page 439
W90P710CD/W90P710CDG
Publication Release Date: September 19, 2006
- 439 -
Revision B2
6.16.2 RTC Application Note
Detect RTC frequency
Step1. Configure GPIO register GPIOCFG5[21:20] as “2’b11”
Step2. Making use of frequency counter (for example: Agilent 53131A) to detect W90P710 IO Pin
“GPIO15/nWDOG/USBPWREN”.
Note: Because the parasitic capacitance would slow crystal oscillation, do not connect the probe with
32K crystal directly.
RTC application circuit
1.
The recommended RTC appliction circuit is ad following:
EXTAL32
XTAL32
RTCVDD1.8V
C1
C2
2.
C1 and C2 can not be connected to ground for improving noise issue.
3.
Do not connect any register in the circuit. Redundant register may stop crystal oscillation.
4.
To avoid parastic capacitance and resistance, user had better to place all components as close
as possible.
5.
The C1 and C2 vaule would be changed by different crystal because different crystal requires
different oscillation condition. In general, capacitance value of C1/C2 is between 10pF and 30pF.