Maxim Integrated MAXQ7667 - Manual (Page 254)

__________________________________________________________________________________________________________ 15-2
MAXQ7667 User’s Guide
SECTION 15: OSCILLATOR/CLOCK GENERATION
The MAXQ7667 oscillator/clock generation module is the clock generator that supplies the system clock for the microcontroller core
and all the peripheral modules.
The oscillator is designed to allow flexibility for selecting a timing source for the MAXQ7667 microcontroller. The MAXQ7667 clock
source can be derived from the following:
• Internal RC oscillator with a maximum of 16MHz frequency (factory default setting is 13.5MHz; no external crystal or oscillator
source required)
• Internal high-frequency oscillator driving an external 2.0MHz to 16.0MHz crystal or ceramic resonator
• External high-frequency 2.0MHz to 16.0MHz oscillator input
• External oscillator/crystal source failure detection and automatic switchover to the internal RC oscillator
• Crystal warmup timer to assure that the internal digital core voltage (DVDD) has reached appropriate level
• Watchdog timer
• Low-power stop state
15.1 Architecture
The MAXQ7667 is designed to operate from 2MHz up to 16MHz of external high-frequency source. Because of its RISC-based design,
the MAXQ7667 executes most instructions in a single system clock (SYSCLK) period. All functional modules (SPI, timer/counter, SAR
ADC, etc.) are synchronized to this single system clock. This system clock is derived from one of the following possible sources:
• Internal RC oscillator running at a maximum of 16MHz with a default value of approximately 13.5MHz. This frequency could be
trimmed by the user, but it is subject to minor variation due to voltage and temparature.
• External high-frequency oscillator clock
• External high-frequency crystal (with an internal oscillator)
15.2 Oscillator/Clock Status and Control Registers
Six registers control the oscillator/clock configuration, report status, and control operation in the MAXQ7667. Three of the registers are
found in the peripheral register bank in Module 05h, indexes 05h, 08h, 0Bh; two registers are found in the system register bank in
Module 08h, indexes 0Eh and 0Fh; and one register is found in Module 01h, index 17h. The registers are:
Peripheral Registers
• Analog Interrupt Enable Register (AIE): Module 05h, Index 05h
• Analog Status Register (ASR): Module 05h, Index 08h
• Oscillator Control Register (OSCC): Module 05h, Index 0Bh
System Registers
• System Clock Control Register (CKCN): Module 08h, Index 0Eh
• Watchdog Timer Control Register (WDCN): Module 08h, Index 0Fh
• RC Oscillator Trim Register (RCTRM): Module 01h, Index 17h