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ST7LITEUS5 数据表(PDF) 54 Page - STMicroelectronics |
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ST7LITEUS5 数据表(HTML) 54 Page - STMicroelectronics |
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54 / 136 page  Obsolete Product(s) - Obsolete Product(s) Obsolete Product(s) - Obsolete Product(s) Power saving modes ST7LITEUS2, ST7LITEUS5 54/136 Halt mode recommendations ● Make sure that an external event is available to wakeup the microcontroller from Halt mode. ● When using an external interrupt to wakeup 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). 8.5 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 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 divider and a programmable prescaler controlled by the AWUPR register. The output of this prescaler provides 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. AWU RC AWUFH fAWU_RC AWUFH (ei0 source) oscillator prescaler/1 .. 255 interrupt /64 divider to 8-bit Timer input capture Obsolete Product(s) - Obsolete Product(s) |
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