参数资料
型号: ST7PLITEUS5M6TR
厂商: STMICROELECTRONICS
元件分类: 微控制器/微处理器
英文描述: 8-BIT, MROM, 8 MHz, MICROCONTROLLER, PDSO8
封装: 0.150 INCH, LEAD FREE, PLASTIC, SOP-8
文件页数: 40/108页
文件大小: 1957K
代理商: ST7PLITEUS5M6TR
ST7LITEUSx
37/108
POWER SAVING MODES (Cont’d)
8.4.2.1 HALT Mode Recommendations
– 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 ex-
ternal interference or by an unforeseen logical
condition.
– For the same reason, reinitialize the level sensi-
tiveness of each external interrupt as a precau-
tionary 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 memo-
ry. 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 execut-
ing the HALT instruction. This avoids entering
other peripheral interrupt routines after executing
the external interrupt routine corresponding to
the wake-up event (reset or external interrupt).
8.5 AUTO WAKE UP FROM HALT MODE
Auto Wake Up From Halt (AWUFH) mode is simi-
lar to Halt mode with the addition of a specific in-
ternal RC oscillator for wake-up (Auto Wake-Up
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 realtime
clock available.
It is entered by executing the HALT instruction
when the AWUEN bit in the AWUCSR register has
been set.
Figure 25. AWUFH Mode Block Diagram
As soon as HALT mode is entered, and if the
AWUEN bit has been set in the AWUCSR register,
the AWU RC oscillator provides a clock signal
(fAWU_RC). Its frequency is divided by a fixed divid-
er and a programmable prescaler controlled by the
AWUPR register. The output of this prescaler pro-
vides the delay time. When the delay has elapsed,
the following actions are performed:
– the AWUF flag is set by hardware,
– an interrupt wakes-up the MCU from Halt mode,
– the main oscillator is immediately turned on and
the 64 CPU cycle delay is used to stabilize it.
After this start-up delay, the CPU resumes opera-
tion by servicing the AWUFH interrupt. The AWU
flag and its associated interrupt are cleared by
software reading the AWUCSR register.
To compensate for any frequency dispersion of
the AWU RC oscillator, it can be calibrated by
measuring the clock frequency fAWU_RC and then
calculating the right prescaler value. Measurement
mode is enabled by setting the AWUM bit in the
AWUCSR register in Run mode. This connects
fAWU_RC to the input capture of the 8-bit lite timer,
allowing the fAWU_RC to be measured using the
main oscillator clock as a reference timebase.
AWU RC
AWUFH
fAWU_RC
AWUFH
(ei0 source)
oscillator
prescaler/1 .. 255
interrupt
/64
divider
to 8-bit Timer input capture
1
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