ATAM510X-ILQY ATMEL [ATMEL Corporation], ATAM510X-ILQY Datasheet - Page 15

• Manufacturer Part Number: ATAM510X-ILQY
• Description: MARC4 4-bit MTP Universal Microcontroller
• Manufacturer: ATMEL [ATMEL Corporation]

2.7
2.7.1
4711B–4BMCU–01/05
Clock Generation
Clock Module
The clock module generates two clocks. The system clock (SYSCL) supplies the CPU and the
peripherals while the lower frequency periphery sub-clock (SUBCL) supplies only the peripher-
als. The modes for clock sources are programmable with the OS1-bit and OS0-bit in the SC-
register and the CCS-bit in the CM-register.
The clock module includes 4 different internal oscillator types: two RC-oscillators, one 4-MHz
crystal oscillator and one 32-kHz crystal oscillator. The pins OSC1 and OSC2 provide the inter-
face to connect a crystal either to the 4-MHz, or to the 32-kHz crystal oscillator. SCLIN can be
used as an input for an external clock or to connect an external trimming resistor for the RC-
oscillator 2. All necessary components with the exception of the crystal and the trimming resistor
is integrated on-chip. Any one of these clock sources can be selected to generate the system
clock (SYSCL).
In applications that do not require exact timing, it is possible to use the fully integrated RC-oscil-
lator 1 without any external components. The RC-oscillator 2 is more stable but the oscillator
frequency must be trimmed with an external resistor attached between SCLIN and V
configuration, for system clock frequencies below 2 MHz, the RC-oscillator 2 frequency can be
maintained stable with a tolerance of 10% over the full operating temperature and voltage
range.
The clock module is software programmable using the clock management register (CM) and the
system configuration register (SC). The required oscillator configuration can be selected with the
OS(1:0)-bits in the SC-register. A programmable 4-bit divider stage allows the adjustment of the
system clock speed. A synchronization stage avoids any clock glitches which could be caused
by clock source switching.
The CPU always requires SYSCL clocks to execute instructions, process interrupts and enter or
leave the SLEEP state. Internal oscillators are, depending on the condition of the NSTOP-bit
automatically stopped and started where necessary. Special care must however be taken when
using an external clock source which is gated by one of the microcontroller port signals. This
configuration can hang up if the external oscillator is switched off while the external clock source
is still selected. It is therefore advisable in such a case to switch first to the internal RC-oscillator
1 source using the CSS-bit. The external source can then be reselected later when the external
oscillator has again been restarted.
ATAM510
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