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M44C892
M44C892
M44C092
Rev. A5, 14-Dec-01
19 (84)
System Configuration Register (SC)
Primary register address: ’3’hex
Bit 3
Bit 2
Bit 1
Bit 0
SC: write
BOT
–––
OS1
OS0
Reset value: 1x11b
BOT
Brown-Out Threshold
BOT = 1, low brown-out voltage threshold (1.7 V)
BOT = 0, high brown-out voltage threshold (2.0 V)
OS1
Oscillator Select 1
OS0
Oscillator Select 0
Mode
OS1
OS0
Input for SUBCL
Selected Oscillators
1
1
1
Cin / 16
RC–oscillator 1 and external input clock
2
0
1
Cin / 16
RC-oscillator 1 and RC-oscillator 2
3
1
0
Cin / 16
RC-oscillator 1 and 4-MHz crystal oscillator
4
0
0
32 kHz
RC-oscillator 1 and 32-kHz crystal oscillator
If the bit CCS = 0 in the CM-register the RC-oscillator 1 always stops.
2.6
Power-down Modes
The sleep mode is a shut-down condition which is used to
reduce the average system power consumption in applica-
tions where the
C is not fully utilized. In this mode, the
system clock is stopped. The sleep mode is entered via the
SLEEP instruction. This instruction sets the interrupt en-
able bit (I) in the condition code register to enable all
interrupts and stops the core. During the sleep mode the
peripheral modules remain active and are able to generate
interrupts. The
C exits the sleep mode by carrying out
any interrupt or a reset.
The sleep mode can only be kept when none of the inter-
rupt pending or active register bits are set. The application
of the $AUTOSLEEP routine ensures the correct function
of the sleep mode. For standard applications use the $AU-
TOSLEEP routine to enter the power-down mode. Using
the SLEEP instruction instead of the $AUTOSLEEP fol-
lowing an I/O instruction requires to insert 3 non I/O
instruction cycles (for example NOP NOP NOP) between
the IN or OUT command and the SLEEP command.
The total power consumption is directly proportional to
the active time of the
C. For a rough estimation of the
expected average system current consumption, the fol-
lowing formula should be used:
Itotal (VDD,fsyscl) = ISleep + (IDD
tactive / ttotal)
IDD depends on VDD and fsyscl.
The M44C092
/ M44C892 has various power-down
modes. During the sleep mode the clock for the MARC4
core is stopped. With the NSTOP-bit in the clock manage-
ment register (CM) it is programmable if the clock for the
on–chip peripherals is active or stopped during the sleep
mode. If the clock for the core and the peripherals is
stopped the selected oscillator is switched off. An excep-
tion is the 32-kHz oscillator, if it is selected it runs
continously independent of the NSTOP-bit. If the oscilla-
tor is stopped or the 32 kHz oscillator is selected, power
consumption is extremely low.
Table 6 Power-down modes
Mode
CPU Core
Osc-Stop*
Brown-out
Function
RC-Oscillator 1
RC-Oscillator 2
4-MHz Oscillator
32-kHz
Oscillator
External Input
Clock
Active
RUN
NO
Active
RUN
RUN
YES
Power-down
SLEEP
NO
Active
RUN
RUN
YES
SLEEP
SLEEP
YES
STOP
STOP
RUN
STOP
* Osc-Stop = SLEEP & NSTOP & WDL