Should I use an external brownout detector / supply voltage monitor with my Silicon Labs MCU?
All Silicon Labs MCUs have an internal brown out detector / supply voltage monitor. In most cases, the internal supply monitor is sufficient and an external supply monitor is not required.
However, an external supply monitor is recommended for devices where the supply monitor's reset threshold is below the minimum required supply voltage.
For example, the C8051F36x's supply voltage must be between 3.0V and 3.6V when SYSCLK > 50 MHz:
And the supply monitor's reset threshold is 2.55V typical:
For SYSCLK > 50 MHz and the typical case reset threshold, the MCU will be operating out of specification and unpredictably when the supply voltage is between 2.55V and 3.0V. Therefore, an external supply monitor should be used to reset the MCU when the supply voltage reaches 3.0V. This guarantees that MCU operation is within specification and predictable at all times.
ADC readings using VREF, such as the internal temperature sensor, take 200 ms or more to stabilize
Internal temperature reading is incorrect for the first few seconds after power up
Affected devices: C8051F38x
The on-chip reference buffer has a quick turn-on time of about 3 ms when using the recommended 4.7 uF tantalum and 0.1 uF ceramic bypass capacitors.
The reference can source current to quickly charge the bypass capacitors from 0 V to the VREF output voltage in the specified turn-on time.
However, the reference is unable to quickly sink current to discharge the bypass capacitors from voltages above the VREF output voltage.
Since port pins, during power-on reset, are open-drain, hi-impedance with a weak pull up to VIO/VDD, the reference bypass capacitors can potentially charge up to VIO/VDD until the MCU exits POR and the VREF pin is configured for analog mode. Once the bypass capacitors are fully charged to VIO/VDD, it can take several hundred milliseconds to discharge the capacitors back down to VREF. Analog measurements taken while VREF is settling will be very inaccurate.
Since the reference buffer can't sink current quickly, it is recommended to short the VREF pin to ground after POR (driving the pin low) to discharge the VREF bypass capacitors. Once the capacitors have been discharged below VREF, the pin can be configured for analog mode and the reference buffer can be enabled to quickly charge the capacitors up to VREF.
How do I construct a CP2114 DAC configuration string?
The DAC configuration string accepted by the CP2114 configuration utility (AN712) consists of 3 parts. To explore how each operates let's take a look at the configuration for the CS42L55 which can be found in the file CP2114_config_0_CS42L55.txt
The first part of the configuration string is 30 bytes long. It contains CP2114 settings as described in Table 23 (section 9.1.4) of the CP2114 Datasheet.
This guide will walk through creating and configuring a project for a C8051 MCU. This example uses a C8051F930 MCU and the F93x_Blinky example project that is bundled with the Silicon Labs 8-bit IDE and Simplicity Studio.
1. First, create a new project by navigating to Project -> Create New Project...
2. Choose 8051 as the Tool chain, and C project as the project template.
3. Add the project's source files to the project. The F93x_Blinky example here was found in the \Examples directory of the Silicon Labs 8-bit IDE install directory - the default directory for this file is C:\Silabs\MCU\Examples\C8051F93x_92x\Blinky.
4. Point the compiler to the appropriate include directories. This is done through the project Options window, which is accessed by first highlighting the base project in the Workspace window, then navigating the Project -> Options, or by using ALT-F7. In my example, the compiler_defs.h and C8051F930_defs.h files are found within C:\Silabs\MCU_2\INC, so I add this directory to the include path.
6. Configure the debug tools. In the same Options window, navigate to the Debugger tab and select "Silabs" as the Driver.
7. Additional configuration is required in the Silabs tab. If using a USB debugger, "USB interface" and "SiLabs 2-wire (C2) interface" must be checked. If powering the device from the debugger, "Continuously power target" must be checked. Additionally, the flash page size must be set to match the size of the MCU. In the case of the C8051F93x series, this page size is 1024 bytes. See the Flash Memory section of the MCU's datasheet for this value.
8. The project setup should be complete. Selecting "Download and Debug" should successfully build and download the project to the connected device.
Why do I get the following error when using the Capacitive Sensing library on the F99x when trying to increase the number of sensors:
*** ERROR L107: ADDRESS SPACE OVERFLOW
The F99x device has 256 bytes of XRAM. The capacitive sensing library needs RAM to store internal variables for excellent capacitive sensitivity, robustness, and dynamic runtime thresholds. The RAM usage scales up with number of sensors as defined in:
The library running on the F99x currently supports up to 2 sensors given the amount of RAM. The F97x is also supported by the capacitive sensing library and has 8 KB of XRAM, which would support more sensors.