MCU speed selection advice

Thread Starter

ak52

Joined Oct 15, 2014
195
Hi guys,

I have a basic doubt regarding speds of MCUs,
In general (all MCU brands included),is it better to use a 16 bit MCU with a higher clock speed or a 32 bit MCU with a lower clock speed?
I know this question is application dependant ,but i would appreciate it if i get a detailed reply on this :)

AK
 

Thread Starter

ak52

Joined Oct 15, 2014
195
hi thanks for the document,but it does not clear my doubt on 16bit@higher clock vs 32bit@lower clock !
 

MrChips

Joined Oct 2, 2009
19,727
Depends on the application. What does the code do?
Are you simply processing 8-bit data?
Or are you doing 64-bit arithmetic?

Are you looking for faster throughput?
A 32MHz MCU will be twice as fast as a 16MHz MCU.

Depending on the architecture of the machine, word length, instruction set, CISC or RISC, von Neumann or Harvard, you might gain some throughput. If the 32-bit machine is three times more efficient than the 16-bit machine then the 32-bit at half the clock speed would win.

There are way too many variables hence all bets are off.

The only way to find out is to try it both ways and compare.
 

Thread Starter

ak52

Joined Oct 15, 2014
195
For example,
16bit MCU running at 80MHz vs a 32bit MCU running at 25MHz --->Which MCU would be usefull for an inverter application.

Another example
An 8 bit MCU running at 16Mhz vs a 32bit MCU runnig with an internal oscillator of 30KHz --->for a simple RTD sensor ,which MCU will be better?

I am looking for faster calculation and reduction in cycle time with preferably less power consumption
 

MrChips

Joined Oct 2, 2009
19,727
There are no definitive answers to your question.

If you want lowest power consumption, the 30kHz MCU would win.
But for ultimate lowest power, use an MCU in STOP mode and lowest current drain.
 

Sensacell

Joined Jun 19, 2012
2,504
The answer is very difficult to arrive at, many variables to consider.

Some applications require more data shuffling and I/O manipulation, rather than raw calculation power, in this case an 8 bit machine could hold it's own against a 32 bit one.

On the other hand, if your code does heavy multi-byte number crunching, then the 32 bit one wins.

For other signal processing tasks, a 16 bit machine with a MAC engine would beat the 32 bit...

Show me a simple answer, and I'll show you a poorly understood question...
 

NorthGuy

Joined Jun 28, 2014
611
MCU is a combination of CPU and periphery modules. Although CPU has some importance, the most important part is periphery because the most critical tasks are performed by periphery.

For example,
16bit MCU running at 80MHz vs a 32bit MCU running at 25MHz --->Which MCU would be usefull for an inverter application.
That would be an MCU with appropriate PWM modules and suitable ADC.

An 8 bit MCU running at 16Mhz vs a 32bit MCU runnig with an internal oscillator of 30KHz --->for a simple RTD sensor ,which MCU will be better?
The MCU which has adequate ADC module (which can operate at given speed and with given accuracy).

I am looking for faster calculation and reduction in cycle time with preferably less power consumption
It depends on the calculations you want to perform. Some MCUs have special provisions for doing some sorts of calculations. For example MCU with DSP capabilities will perform DSP processing much more efficiently. Floating point calculations will be more efficient on MCU with FPU. Etc.

Also, more precision in your calculations is likely to produce more power consumption.
 
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