LTC5800-IPR View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC5800-IPR' PDF : 28 Pages View PDF
Advanced Information
4.2
Serial Flash Emulation
When both RESETn and FLASH_P_ENn are asserted, Eterna disables normal operation and enters a mode to emulate the
operation of a serial flash. In this mode, its flash can be programmed with software updates. For details, see Section 2.10.
4.3
Operation
Once Eterna has completed startup, Eterna transitions to the Operational group of states (active / CPU active, active / CPU
inactive, and Doze). There, Eterna cycles between the various states, automatically selecting the lowest power state possible
while fulfilling the demands of network operation.
4.3.1
Active State
In Active state, the Eterna’s relaxation oscillator is running and peripherals are enabled as needed. The ARM Cortex-M3
cycles as needed between CPU-active and CPU-inactive (referred to in the ARM Cortex-M3 literature as “Sleep Now” or
“Sleep on Exit” modes). Eterna’s extensive use of DMA and intelligent peripherals that can independently move Eterna
between the Active and Doze states minimizes the time the CPU is active, significantly reducing Eterna’s energy
consumption.
4.3.2
Doze State
The Doze state consumes orders of magnitude less current than the Active state (see Table 6) and is entered when all of the
peripherals, save the low power portion of the timer module, and the CPU are inactive. In the Doze state Eterna’s full state is
retained and Eterna is configured to detect, wake, and rapidly respond to activity on I/Os (such as UART signals and the
TIMEn pin). The Doze state also uses the 32.768-kHz oscillator and 32 kHz based timers are active.
4.4
Duty Cycling and Autonomous Peripherals
Eterna’s ability to quickly and efficiently transition between Doze and Active states, in conjunction with the ability of
peripherals to operate autonomously for most operations (shown in Figure 9), enables the system solution to significantly
reduce power consumption. For example the system can automatically go from Doze to Active and determine if RF energy is
present. The CPU is then only woken if a packet is detected, otherwise Eterna returns to Doze mode.
Figure 9 Low Energy Duty Cycling
Eterna Datasheet
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