I recently posted a blog entry about the Quick Design Guide for the RX610. RX62N, and RX621 microcontrollers (MCUs) that Renesas recently released. That document truly offers easily digestible details as I chronicled in describing the RX memory map. Today I’ll present more about the RX approach to reducing power consumption via information in the guide. We’ll focus on the five operating modes that the RX supports that allow the MCU to enter various low-power modes when the task at hand allows.
Most everyone is familiar with the concept of a sleep mode in computers because we experience that concept regularly in using PCs. Embedded applications, however, offer far greater potential to save energy through a more granular set of low-power modes that a processor can enter based on the task load. Indeed the RX supports five such modes.
The RX modes range from full power and maximum performance to Deep software standby mode from which recovery to full operation is equivalent to a reset function. As you step through the five stages, power consumption goes down while the time it takes to recover from the sleep mode goes up. The modes are:
- Normal program execution
- Sleep mode
- All-module clock stop mode
- Software standby mode
- Deep software standby mode.
The figure below details the state of the processor in each mode and the state of peripherals and key functions such as the real-time clock.
As you peruse the table above, you may note quite a few reference to foot notes and if you want more detailed information you should review the deign guide. But to give you an idea of what you would find in the guide, consider the second row of information that details how the processor can be awakened.
Any interrupt can awaken the processor from Sleep mode. Any external interrupt can awaken the processor from the All-module clock stop mode and the Software standby mode. Some internal interrupts such as the real-time clock can also awaken the processor in the same two modes although the list gets shorter in the latter mode. Only a short list of internal interrupts can awaken the processor from Deep software standby mode.
If you want to learn more about low-power modes, consider attending the upcoming Renesas DevCon. On Thursday Oct 14 at 8:30 AM, there is a session entitled “Optimizing RX Performance.” That session will focus on the tradeoff between performance and power consumption and will cover all of the low-power modes in detail as well as other issues such as clock and device settings.
In a future post we’ll take a look at the power savings achievable in each mode.