EM6621 Datasheet, PDF (6/69 Pages) EM Microelectronic - MARIN SA – Ultra Low Power Microcontroller with 4x20 LCD Driver

EM6621
2. Operating Modes
The EM6621 has two low power dissipation modes, standby and sleep.
these modes.
Figure 4 is a transition diagram for
2.1 Active Mode
The active mode is the actual CPU running mode. Instructions are read from the internal ROM and executed by
the CPU. Leaving active mode via the halt instruction to go into standby mode, the Sleep bit write to go into
Sleep mode or a reset from port A to go into reset mode.
2.2 Standby Mode
Executing a halt instruction puts the EM6621
into standby mode. The voltage regulator,
oscillator, watchdog timer, LCD, interrupts,
timers and counters are operating. However,
the CPU stops since the clock related to
instruction execution stops. Registers, RAM
and I/O pins retain their states prior to
standby mode. A reset or an interrupt request
if enabled cancels standby.
Figure 4 Mode transition diagram
Halt
instruction
Active
Standby
IRQ
Reset=1
Reset=0
Sleep bit
write
Sleep
2.3 Sleep Mode
Writing to the Sleep bit in the RegSysCntl1
register puts the EM6621 in sleep mode. The
Reset=1
Reset=1
oscillator stops and most functions of the
EM6621 are inactive. To be able to write to
Reset
the Sleep bit, the SleepEn bit in
RegSysCntl2 must first be set to "1". In
sleep mode only the voltage regulator and the reset input are active. The RAM data integrity is maintained.
Sleep mode may be canceled only by a high level of min 10µs at the EM6621 Reset terminal or by the selected
port A input reset combination, if option InpResSleep is turned on.
Due to the cold-start characteristics of the oscillator, waking up from sleep mode may take some time to
guarantee stable oscillation. During sleep mode and the following start up the EM6621 is in reset state. Waking
up from sleep clears the Sleep flag but not the SleepEn bit. Inspecting the SleepEn allows to determine if the
EM6621 was powered up (SleepEn = "0") or woken up from sleep (SleepEn = "1").
Table 2.3.1. Internal State in Standby and Sleep Mode
Function
Oscillator
Oscillator Watchdog
Instruction Execution
Interrupt Functions
Registers and Flags
RAM Data
Option Registers
Timer & Counter
Logic Watchdog
I/O Port B and Serial Port
Input Port A
LCD
Strobe Output
Buzzer Output
Voltage Level Detector
Reset Pin
Standby
Active
Active
Stopped
Active
Retained
Retained
Retained
Active
Active
Active
Active
Active
Active
Active
Finishes ongoing measure, then stop
Active
Sleep
Stopped
Stopped
Stopped
Stopped
Reset
Retained
Retained
Reset
Reset
High Impedance,
Pull’s as defined in option register
No pull-downs and inputs deactivated
except if InpResSleep = "1"
Stopped (display off)
Active
High Impedance
Stopped
Active
© EM Microelectronic-Marin SA, 03/99, Rev. B/
Copyright  2002, EM Microelectronic-Marin SA
6
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