Maxim Integrated MAXQ Family Users Guide: MAXQ8913 Supplement - Manual (Page 15)

MAXQ Family User’s Guide:
MAXQ8913 Supplement
2-6
2.6.2 Ring Oscillator
The MAXQ8913 contains an internal ring oscillator that can optionally be used as a system clock. The ring oscillator
operates at a frequency of approximately 1MHz (refer to the MAXQ8913 data sheet for details).
On power-on reset, the ring oscillator is automatically enabled as the system clock source while the high-frequency
oscillator warms up. Once the warmup count for the high-frequency oscillator has completed, the clock source switch-
es to the high-frequency oscillator automatically. If no external crystal or resonator circuit is provided at HFXIN, the
switchover never occurs, and the clock runs from the ring oscillator indefinitely.
To explicitly select the ring oscillator as the system clock source, the RGSL bit (CKCN.6) must be set to 1. Setting this
bit switches over the system clock source to the ring oscillator following a 10-cycle delay of the 1MHz ring clock. The
RGMD (CKCN.5) bit indicates the current system clock source. If the ring oscillator is currently providing the system
clock, RGMD reads as 1; otherwise, RGMD reads as 0.
Figure 2-5. MAXQ8913 Clock Sources
GLITCH-FREE
MUX
GLITCH-FREE
MUX
CLOCK
DIVIDER
SELECTOR
DEFAULT
RING SELECT
DIV 1 DIV 2 DIV 4 DIV 8 PMM
WATCHDOG
TIMER
RESET DOG
RWT
RESET POWER-ON
RESET
STOP
STOP
POWER-ON
RESET
SWB
SWITCHBACK SOURCES
RESET
STOP
RGSL
XDOG DONE
RGMD
POWER-ON RESET
WATCHDOG RESET
CLOCK
GENERATION
SYSTEM CLOCK
ENABLE
WATCHDOG INTERRUPT
1MHz
INTERNAL
RING OSC
ENABLE
CRYSTAL
MONITOR
ENABLE
INPUT
HF
CRYSTAL
CRYSTAL KLL
XDOG
STARTUP
TIMER
CLK INPUT
RESET XDOG COUNT
XDOG DONE
MAXQ8913
Maxim Integrated