In some cases, it is desirable to use the integrated charge pump when operating in the low power modes to power certain peripherals, such as the Real Time Clock (RTC). The SiM3L also integrates a missing clock detector that detects an RTC0 Oscillator Fail event when the RTC0 Missing Clock Detector is enabled and the RTC0OSC falls below the missing clock detector trigger frequency. When enabled, the charge pump powers the RTC and also uses the RTC clock as its pump clock to generate the voltage. If the RTC has a failure (such as losing the clock), the charge pump will also fail, thereby disabling power to the RTC. It is expected that firmware must disable the charge pump, restart the RTC, then re-enable the charge pump once the RTC is up and running.
The 5VDIFF mode can be used for differential signals (-2.5V to 2.5V) or single ended signals (0V to 2.5V). The value of the LSB does not change between these modes.
The reference is created by using an internal reference of 0.83V with a voltage divider of 1/6. This results in the measured signal being effectively compared to a 5V reference. The input to the ADC pin is still limited by the supply rails.
How can I avoid "ground bounce" when using the SiM3U1xx or SiM3C1xx high drive I/O?
Our high current drivers have both programmable current limiting and four levels of programmable slew rate, which can mitigate the effects of ground bounce. If you set the slew rate limiting to the slowest setting, you will have no ground bounce issues if the MCU is properly grounded and you are driving a capacitive (non-inductive) load.
How many I/O can concurrently drive 300mA on SiM3U1xx?
Our devices can sink a maximum of 300 mA and source a maximum of 150 mA. The maximum sink or source for all I/Os on one supply is 400 mA. In other words, all I/Os in source mode must total less than 400 mA and all I/Os in sink mode must total less than 400 mA.
Which Silicon Labs STKs are mbed enabled and how can I tell?
All of the Silicon Labs EFM32 STKs support the mbed eco-system. After connecting the USB cable for the debug interface you should see a new Mass Storage drive created in Windows. If the drive is not displayed, select the Kit Manager in the Simplicity Studio tile screen and update the STK firmware. Once complete the drive should appear.
Pearl and Jade Gecko devices integrate a crypto accelerator. What is the best way for me to take advantage of the accelerator and implement my own cryptography?
The crypto accelerator significantly reduces the clock cycles required to implement standard crypto algorithms. Since advanced cryptography systems tend to be very complex and the development time to create such systems can be very long, Silicon Labs recommends using a standard set of libraries that have been proven in the industry. ARM provides the mbedTLS libraries (formerly PolarSSL) that support many of the standard encryption/decryption algorithms and cipher modes in wide use today. These libraries can be used "stand-alone" and do not need to use the mbed platform and online services.
Since the mbedTLS libraries do not have any awareness of the crypto accelerator, we have provided our own crypto libraries to be used with the mbedTLS libraries. In order to take advantage of the crypto accelerator the mbedTLS libraries, based on compile time options, will instead use the Silicon Labs libraries that offload the computationally intensive crytpo algorithms from the CPU to the crypto engine, significantly increasing performance while reducing power consumption.
Several example projects are included in the Simplicity Studio tools to illustrate how to use the CRYPTO module for both symmetric (CBC-AES) and asymmetric (ECDSA) encryption. In addition, application note AN0955: CRYPTO covers the different libraries and their uses.