Tag Archives: AVR


In embedded systems, oftentimes it is needed to generate analog outputs from a microcontroller. Examples of such include, generating audio tones, voice, music, smooth continuous waveforms, function generators, voltage reference generators, etc. Traditionally in such cases the most common techniques applied are based on Pulse Width Modulation (PWM), resistor networks and external Digital-to-Analog Converter (DAC) chips like MCP4921. The aforementioned techniques have different individual limitations and moreover require external hardware interfacing, adding complexities and extra cost to projects.  XMega micros are equipped with 12 bit fast DACs apart from PWM blocks and again it proves itself to be a very versatile family of microcontrollers. In this post we will have a look into this block.

DAC Internal Block Diagram

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XMega External Interrupt

External interrupts are a must have feature in any microcontroller. Interrupts solve a lot of problem that would have otherwise been dependent on polling methods. For instance when we press the volume up key of a TV tuner’s remote controller, the remote controller quickly responds by transmitting the volume up command to the TV set and in turn the TV’s volume increases. This fast response is due to external interrupt issued by the remote’s button to the microcontroller it is connected to. If, however, all the keys of the remote were regularly and frequently scanned and then responded up on a press, the process would have been both slow and energy consuming because its microcontroller would then have never went to sleep or low power states and continuously kept scanning. In other words, the micro would have always ran despite no mandatory necessity and during standby conditions. This would have quickly drained the batteries. Since interrupt is typically used in such cases the remote controller will respond to a button press fast, wake up from sleep/idle/low power mode, transmit command data and then go back to sleep/idle/low power state. Thus the overall energy consumption is reduced while achieving fastest possible reaction. This is how real world applications work applying external interrupts.

XMega 3D


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XMega Analog Comparator

Previously we dealt with the XMega Analog-to-Digital Converter (ADC) block. We know that we can use the ADC to measure voltages and take decisions based on voltage values/levels but sometimes it is enough to detect voltage levels and not to measure the exact voltage values. In such occasions where we just need to check voltage levels relative to a reference or threshold value, we need an Analog Comparator (AC). An analog comparator can be used to compare two voltage levels and based on that it can be used to generate a logic output (0 or 1) to indicate which of the two levels is higher or lower than the other. That’s all and there isn’t much about analog comparators. The XMega family of micros come loaded with high performance dual analog comparator modules. However so far we saw that between the traditional 8-bit micros and the XMega micros, the major difference apart from programming is the overall nifty enhancements in all common hardware blocks. When it comes to the analog comparators of the XMega micros, the same is true. In this issue we will explore the XMega analog comparator block.

Block Diagram


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For users of advance MCUs like the XMega it is not necessary to tell what an analog-to-digital converter (ADC) is or what it does. I assume this is not the first family of microcontroller they are dealing with. Unlike the ADCs of other microcontroller the ADC of XMega devices is a highly complex tool. The level of complexity is so much that without understanding every bits-and-pieces of this piece of hardware a user won’t enjoy its absolute power. XMega ADC is also the most confusing hardware as it is not like other MCU ADCs. We will be dealing with ATXMega32A4U and it has only one ADC block, named ADCA but some other XMega devices like the XMega128A1 have more than one ADC block – ADCA and ADCB. By the way the XMega reference manual provides a long literature on the ADC and I’m not willing to state everything.

A quick view of the ADC block diagram shows most of the internal arrangement.

ADC internal

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ATXMega Primer

The XMega series is a powerful addition to the existing arsenal of Atmel’s AVR-core micros. As much as I have personally studied about it so far and felt, the XMega series incorporates many features of conventional 32-bit ARM micros like alternate I/O pin mapping functionalities, sophisticated clock options and data buses, multiple communication platforms that have several uses, variety of capture-PWM options, 12-bit ADCs and DACs, DMA controller, USB hardware, etc. with the good old AVR core. Thus you get one hell of an 8/16 bit MCU that can fulfil your wildest micro desires. In terms of unit cost, resources and user flexibilities this family of micro can beat any present day micro in most of the scenarios. Unlike other manufacturers who design chips as to fit specific applications, there’s no limit for XMega series. It is one controller with unlimited possibilities that can fit into any application. Indeed it is a true Atmel slogan now:

My microcontroller can beat the hell out of your microcontroller.”

There are several things that are should be known. XMega is still a relatively new breed of micro. There’s literally nothing similar to it in the market no matter which manufacturer you can name. As I said Atmel added literally everything that can be imagined. Initial XMega devices had several hardware flaws and were unstable. They had problems related to power and operational stability. However these shortcomings are no longer there as they were. Atmel dramatically improved this new line of devices and are yet doing a lot of R&D on it. The older successful AVR Mega series micros are not as same as XMegas and so what can be applied to Mega AVR can’t be applied for the XMegas. There are significant differences both in terms of hardware and software but still there are similarities.
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