EM6520 EM Microelectronic, EM6520 Datasheet - Page 6

• Manufacturer Part Number: EM6520
• Description: MFP version of EM6620 Ultra Low Power Microcontroller 4x8 LCD Driver
• Manufacturer: EM Microelectronic

2
The EM6520 has two low power dissipation modes, standby and sleep. Figure 4 is a transition diagram for
these modes.
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 the active mode: via the halt instruction to go into standby mode, writing the SLEEP bit to go
into Sleep mode or detecting the reset condition from port A to go into reset mode.
2.2 STANDBY Mode
Executing a HALT instruction puts the EM6520 into
standby mode. The voltage regulator, oscillator,
watchdog timer, LCD, interrupts, timers and counters
are operating. However, the CPU stops since the
clock
Registers, RAM and I/O pins retain their states prior
to STANDBY mode. STANDBY is canceled by a
RESET or an Interrupt request if enabled.
2.3 SLEEP Mode
Writing to the Sleep bit in the RegSysCntl1 register
puts the EM6520 in sleep mode. The oscillator stops
and most functions of the EM6520 are inactive. To
be able to write to the Sleep bit, the SleepEn bit in
RegSysCntl2 must first be set to "1". In SLEEP
mode only the voltage regulator is active to maintain
the RAM data integrity, all other functions are in
reset state. SLEEP mode may be canceled only by
the input reset combination from port A
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 EM6520 is in reset state. Waking
up from sleep mode clears the Sleep flag but not the SleepEn bit. Inspecting the SleepEn allows to determine if
the EM6520 was powered up (SleepEn = "0") or woken from sleep mode (SleepEn = "1").
TAKE CARE !!! To quit sleep mode, one must be sure to have a suitable defined combination of port A inputs
for reset (see section 4.2). The Bit NoInpReset has no action during sleep mode.
Table 2.3.1 Shows the state of the EM6520 functions in STANDBY and SLEEP modes
Copyright  2002, EM Microelectronic-Marin SA
Operating modes
Voltage Level Detector
Instruction execution
Oscillator supervisor
related
Registers and flags
Interrupt functions
Timer/Counter's
Option registers
Logic watchdog
FUNCTION
Input port A
RAM data
I/O port B
Oscillator
LCD
to
instruction
execution
NoInputRes = "0" for reset generation
finishes on going measure, then stop
.
stops.
STANDBY
Retained
Retained
Retained
Stopped
Active
Active
Active
Active
Active
Active
Active
Active
Figure 4 Mode transition diagram
Standby
6
instruction
Reset=1
Halt
IRQ
Reset=1
Only active for Reset generation
High Impedance, Pull resistors
Active
Reset
Stopped (display off)
NoInputRes = "X"
Reset=0
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as defined
Retained
Retained
Stopped
Stopped
Stopped
Stopped
Stopped
EM6520
SLEEP
Reset
Reset
Reset
Reset=1
Sleep bit
write
03/02 REV. D/449
Sleep