MSP430G2955
MSP430G2855
MSP430G2755
SLAS800 –MARCH 2013
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Peripherals
Peripherals are connected to the CPU through data, address, and control buses and can be handled using all
instructions. For complete module descriptions, see the MSP430x2xx Family User's Guide (SLAU144).
Oscillator and System Clock
The clock system is supported by the basic clock module that includes support for a 32768-Hz watch crystal
oscillator, an internal very-low-power low-frequency oscillator and an internal digitally controlled oscillator (DCO).
The basic clock module is designed to meet the requirements of both low system cost and low power
consumption. The internal DCO provides a fast turn-on clock source and stabilizes in less than 1 µs. The basic
clock module provides the following clock signals:
•
•
•
Auxiliary clock (ACLK), sourced either from a 32768-Hz watch crystal or the internal LF oscillator.
Main clock (MCLK), the system clock used by the CPU.
Sub-Main clock (SMCLK), the sub-system clock used by the peripheral modules.
The DCO settings to calibrate the DCO output frequency are stored in the information memory segment A.
Main DCO Characteristics
•
All ranges selected by RSELx overlap with RSELx + 1: RSELx = 0 overlaps RSELx = 1, ... RSELx = 14
overlaps RSELx = 15.
•
•
DCO control bits DCOx have a step size as defined by parameter SDCO.
Modulation control bits MODx select how often fDCO(RSEL,DCO+1) is used within the period of 32 DCOCLK
cycles. The frequency fDCO(RSEL,DCO) is used for the remaining cycles. The frequency is an average equal to:
32 × f
× f
DCO(RSEL,DCO+1)
DCO(RSEL,DCO)
f
=
average
MOD × f
+ (32 – MOD) × f
DCO(RSEL,DCO+1)
DCO(RSEL,DCO)
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