MAX32600 User’s Guide
System Clock, Timers/Counters, Watchdog Timers and Real Time Clock
10.1 System Clock
Firmware Control of External High Frequency Clock (Crystal or Resonator)
The external clock is controlled by three fields in the
register. These fields include:
field
Function
HFX Enable
: enables the GM amplifier for the crystal oscillator
HFX Bypass
: permits an external clock to be utilized
HFX GM Adjust
: adjusts the gain current density of the GM amplifier
The following table illustrates the register setting for the most common modes of operation:
HFX GM Adjust
Crystal Frequency
Mode
HFX Enable
HFX Bypass
8MHz
12MHz
24MHz
XTAL Run Mode
1
0
0x05
0x07
0x0A
Disabled
0
0
0x00
External Clock Input
0
1
0x00
Fast XTAL Startup
1
0
0x14
The Crystal oscillator takes from 0.5ms at 24MHz to 2.5ms at 8MHz to start up. Once running, reducing the GM will reduce the current consumption.
10.1.3.3
External 32kHz Clock (Crystal or Resonator)
The
MAX32600
oscillator drives a standard 32.768kHz watch crystal. These crystals are very high-impedance and do not require a high-current oscillator circuit.
The
MAX32600
oscillator is specifically designed to operate with these crystals and is compatible with their high impedance and limited power handling capability.
The oscillator power dissipation is very low in order to maximize the lifetime of the RTC battery.
Note
The oscillator is designed to be self-biasing. An external resistor should not be connected across the crystal.
The oscillator frequency can be adjusted for 25°C accuracy, as well as for temperature effects. See the
section for details.
Rev.1.3 April 2015
Maxim Integrated
Page 504
Содержание MAX32600
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