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MSP430x11x1
MIXED SIGNAL MICROCONTROLLER
SLAS241C – SEPTEMBER 1999 – REVISED JUNE 2000
6
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
status register R2
Reserved For Future
Enhancements
15 9 8 7 0
V SCG1 SCG0 OscOff
CPUOff GIE N Z C
rw-0 rw-0 rw-0 rw-0 rw-0 rw-0 rw-0 rw-0 rw-0 rw-0
6543 21
The bits CPUOff, SCG1, SCG0, and OscOff are the most important low-power control bits when the basic
function of the system clock generator is established. They are pushed onto the stack whenever an interrupt
is accepted and thereby saved so that the previous mode of operation can be retrieved after the interrupt
request. During execution of an interrupt handler routine, the bits can be manipulated via indirect access of the
data on the stack. That allows the program to resume execution in another power operating mode after the
return from interrupt (RETI).
SCG1: The clock signal SMCLK, used for peripherals, is enabled when bit SCG1 is reset or disabled if
the bit is set.
SCG0: The dc-generator is active when SCG0 is reset. The dc-generator can be deactivated only if the
SCG0 bit is set and the DCOCLK signal is not used for MCLK or SMCLK. The current consumed
by the dc-generator defines the basic frequency of the DCOCLK. It is a dc current.
The clock signal DCOCLK is deactivated if it is not used for MCLK or SMCLK or if the SCG0 bit
is set. There are two situations when the SCG0 bit cannot switch off the DCOCLK signal:
1. DCOCLK frequency is used for MCLK (CPUOff=0 and SELM.1=0).
2. DCOCLK frequency is used for SMCLK (SCG1=0 and SELS=0).
NOTE:
When the current is switched off (SCG0=1) the start of the DCOCLK is delayed slightly. The delay
is in the µs-range (see device parameters for details).
OscOff: The LFXT1 crystal oscillator is active when the OscOff bit is reset. The LFXT1 oscillator can only
be deactivated if the OscOff bit is set and it is not used for MCLK or SMCLK. The setup time to
start a crystal oscillation needs consideration when oscillator off option is used. Mask
programmable (ROM) devices can disable this feature so that the oscillator can never be switched
off by software.
CPUOff: The clock signal MCLK, used for the CPU, is active when the CPUOff bit is reset or stopped if it
is set.