ST7LITE49K2 STMicroelectronics, ST7LITE49K2 Datasheet - Page 69

• Manufacturer Part Number: ST7LITE49K2
• Description: 8-bit MCU
• Manufacturer: STMicroelectronics

Specifications of ST7LITE49K2

• 8 Kbytes Single Voltage Extended Flash (xflash) Program Memory With Read-out Protection In-circuit Programming And In-application Programming (icp And Iap) Endurance: 10K write/erase cycles guaranteed Data retention
• 256 Bytes Data Eeprom With Read-out Protection. 300k Write/erase Cycles Guaranteed, Data Retention: 20 years at 55 °C.
• Clock Sources: Internal trimmable 8 MHz RC oscillator, auto-wakeup internal low power - low frequency oscillator, crystal/ceramic resonator or external clock
• Five Power Saving Modes: Halt, Active-halt, Auto-wakeup from Halt, Wait and Slow

ST7LITE49K2
9.5
Halt mode recommendations
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Auto-wakeup from Halt mode
Auto-wakeup from Halt (AWUFH) mode is similar to Halt mode with the addition of a specific
internal RC oscillator for wakeup (Auto-wakeup from Halt oscillator) which replaces the main
clock which was active before entering Halt mode. Compared to Active-Halt mode, AWUFH
has lower power consumption (the main clock is not kept running), but there is no accurate
real-time clock available.
It is entered by executing the HALT instruction when the AWUEN bit in the AWUCSR
register has been set.
Figure 31. AWUFH mode block diagram
Make sure that an external event is available to wake up the microcontroller from Halt
mode.
When using an external interrupt to wake up the microcontroller, reinitialize the
corresponding I/O as “Input Pull-up with Interrupt” before executing the HALT
instruction. The main reason for this is that the I/O may be wrongly configured due to
external interference or by an unforeseen logical condition.
For the same reason, reinitialize the level sensitiveness of each external interrupt as a
precautionary measure.
The opcode for the HALT instruction is 0x8E. To avoid an unexpected HALT instruction
due to a Program Counter failure, it is advised to clear all occurrences of the data value
0x8E from memory. For example, avoid defining a constant in ROM with the value
0x8E.
As the HALT instruction clears the I bit in the CC register to allow interrupts, the user
may choose to clear all pending interrupt bits before executing the HALT instruction.
This avoids entering other peripheral interrupt routines after executing the external
interrupt routine corresponding to the wakeup event (reset or external interrupt).
f
AWU_RC
AWU RC
oscillator
divider
/64
prescaler/1 .. 255
to 8-bit timer Input Capture
AWUFH
(ei0 source)
AWUFH
interrupt
Power saving modes
69/245