Page 82 - ARM Based Microcontroller Projects Using MBED

68 6. ARCHITECTURE OF THE STM32F411RET6 MICROCONTROLLER

• Results stored in data register (or RAM)
• Data preprocessing (left/right alignment) and offset compensation
• Built-in oversampling unit
• Programmable sampling time

6.2.5 Digital-to-Analog Converter (DAC)

Two 12-bit DAC channels are available on the chip. The DAC has the following features:
• 8-bit or 12-bit output mode
• Left/right data alignment (in 12-bit mode)
• Noise-wave generation
• Triangular-wave generation
• Dual DAC independent or simultaneous conversion
• DMA capability
• External triggering
• Sample and hold with internal or external capacitor

6.2.6 Temperature Sensor
A temperature sensor is available on the microcontroller chip that generates voltage line-
arly proportional with temperature. This sensor is internally connected to the ADC_IN18 an-
alog input channel of the microcontroller. The sensor should be calibrated for good accuracy
as its characteristics change from chip to chip due to process variations. The devices are cal-
ibrated at factory by ST where the calibration data are available in the system memory as read-
only data (see the device data sheet).

6.2.7 Timers and Watchdogs
Timer modules are important parts of all microcontrollers. The STM32F411RET6 micro-
controller includes one advanced control timer, seven general purpose timers, two watchdog
timers, and a SysTick timer. Table 6.3 presents a brief summary of the timers.

6.2.8 The Clock Circuit
The clock circuit is an important part of the microcontroller. As shown in Fig. 6.4, there two
system clock (SYSCLK) sources: External clock sources and Internal clock sources.

External Clock Sources
High Speed External (HSE): This can be an external crystal or resonator device, or an ex-
ternal clock signal. The frequency range of the crystal or resonator should be 4–48MHz. It is
recommended to use two capacitors in the range of 4–25pF with the crystal circuit.
When using a clock generator circuit, the waveform can be square, sine, or triangular, and
the waveform must be symmetrical, that is, 50% ON and 50% OFF times. The clock signal
must be fed to the OSC_IN pin of the microcontroller. If external clock circuitry is used, then
HSE oscillator should be bypassed to avoid any conflict.