Why are you still using 8 bit MCUs?

[frank26080115]

By now I have a really good collection of various 8 bit AVR chips and a lot of experience with them. The time I save on each project by knowing what I'm doing is more valuable.

For individual devices, some 32 bit MCUs can certainly compete with their 8 bit MCUs in terms of price. But for a kid like me who needs new tools and a carrier board, it can be expensive to make the switch since JTAG debuggers and dev-boards are very expensive compared to the DIP chip plus a ISP.

DIP packages are too important for inexpensive prototyping, or even inexpensive products. I have sold one-off products for around $40 and I was only able to achieve that price by using off-the-shelf through hole components and perfboarding. A PCB would have added at least $12 more plus 3 more weeks worth of waiting.

I'm not refusing 32 bit MCUs, in fact, my latest project is based around a AT91SAM7XC512, I soldered up my PCB already and got SAM-BA to work like a charm over USB. I just got my Bus Blaster V1 JTAG debugger too. However, this is one of the few projects that actually might require 512KB worth of flash memory, I also might want to mess with .NET Micro Framework.

I'm also getting a mbed (LPC1768) really soon to act as a new 32 bit swiss army knife to replace my 8 bit swiss army knife (the ATmega328P on a USnooBie and Teensy++). It has an ethernet PHY on board and USB host capabilities, unknown territories for me.

[john]

Price and simplicity.
And they are NOT "small"
8 bit on the other hand.
Smallest package is SOT23-6 and plenty available in DIP etc.

So you are basically telling me that you all use 8-bit micros only at 5V and in DIP/SOT packages? That's fine reason, but somehow it is hard for me to believe that no one is using larger 8bit parts,  QFP packages or 3.3V 

Simplicity? Simplicity my ass... I've been using 8051 MCUs for years, and yeah, I could say that they are simple... But it's not MCU itself that's the problem, it's the peripherals! If you have some powerful CAN controller, or even complex PWM module, it doesn't really matter if it is 8 bit or 32 bit MCU, it does require lots of work to configure it properly...  And for startup routines, they are usually autogenerated in IDE or copy/pasted so no real difference there...
It actually gets more ugly on smaller parts, because you often don't have 32 bit registers, and then for example you have to fight with 8 or 16 bit timers, trying to merge several together to get decent resolution when you need it. Or you don't have enough peripherals and there are propably still some guys that would rather do bit banging than use proper MCU... Go figure...

[Mechatrommer]

i sure to keep my option open (with calculated risk ) to this 32bit stuff when i go into more complicated mcu. at least, thanx john for reminding me of this. about the 5V, for me, it gives me more option on what voltage should i use. if say, i have other hardware that needs 3.3V then i can use 3.3V on 8bit mcu, but if its 5V, then i also can use 5V without extra hardware to drop the voltage to 3.3V just for the processor.

[mikeselectricstuff]

Something else which is often a consideration in the high-power electronics that I work with is the operational voltages.

8-bit micros are very simple to obtain with a 5V operating voltage, but the same isn't true of 32-bit micros which generally run at 3.3V or lower.

Good point.
Many in fact need lower rails and have built in low drop regs to power the core that need an external cap.
Is there a 32bit micro at all that runs from 5V? Off the to of my head I can't think of one.

Dave.

Yes - http://www.fujitsu.com/global/services/microelectronics/product/micom/roadmap/industrial/fm3/#a3
From a quick skim of the  datasheet it looks like a 'proper' wide voltage range, not just a cludged-on internal regulator - e.g. all IO and analogue runs on the full supply. Doesn't even look like there are seperate VCCIO pins. Even has an external bus I/F, so you could use old 5V microprocessor peripheral chips - 8255 anyone?
I still think manufacturers are missing a trick by not offering larger pitch lower pin-count devices - onboard voltage reg and 5V IOs would also be really useful - only then will they really be competitive with 8-bit MCUs at the lower end in a lot of applications like white goods.

[Simon]

I heard that excuse couple of times, and I think it's a quite a lame excuse...
How do you define "overkill"? What do you get when you use 8 bit instead of 32 bit? Many 8 bit CPUs are actually more expensive than 32bit, so cost is not the issue (and even if it costs 2-3$ more,  it's hardly an issue for hobby projects)... So, what is?

So your saying you can get me a 32bit MCU in an 8 pin package for less than £0.70 ?

When you write software, there is no such thing as "too fast" CPU  

not neccesarily, infact I totally messed up a project because I did not think that the MCU (at just 4MHz) would easily get ahead of a car engine. I have actually had to put in a delay that lasts vastly longer than the program cycle itself.


On another note, what is this crusade all about ? why do you suppose to tell us what to do ? who are you ?

[mikeselectricstuff]

When you write software, there is no such thing as "too fast" CPU  

Correct, but there are such things "too much power consumption due to unnecessarily fast CPU", as well as "Too high EMI emissions"

[Alex]

Here is an appropriate video

On another note, what is this crusade all about ? why do you suppose to tell us what to do ? who are you ?

Worryingly, John represents a new, ever increasing, breed of engineers entering the field. The phenomenon is much broader.

On the other side of the spectrum, Silicon Labs does 100 MIPS 8-bit MCUs with max core frequency of 100 MHz. They are sucking 65mA at 3.3V. You need to have a good reason to use an 8bit MCU at 100MHZ.

[mikeselectricstuff]

They are still used because it economically makes sense. You may think that 30 cents per micro is nothing but if you are mass producing something in the thousands or millions it doesn’t take long to add-up. So if you spend an extra couple hours in making it work with say a PIC16F690 vs a LPC1111FHN33 that’s more money in your pocket.

Likewise, if you're developing a low volume product, it's often not worth the time to learn a new device if there is a familiar one you can use, even at a higher part cost.

[Simon]

Here is an appropriate video



Worryingly, John represents a new, ever increasing, breed of engineers entering the field. The phenomenon is much broader.

On the other side of the spectrum, Silicon Labs does 100 MIPS 8-bit MCUs with max core frequency of 100 MHz. They are sucking 65mA at 3.3V. You need to have a good reason to use an 8bit MCU at 100MHZ.

Oh dear are we talking about the same breed of engineer that works for microsoft and other software houses that turn out software that gets slower by the hour ? 

Seriously: I have a small automotive project and I have to fit it in a set small space, so I have to use 8 pin nothing any larger than neccesary makes sense, my choice of 8 bit pic as I mentioned earlier has all the speed I need and it may be something i sell, why should i pay over a pound for a larger 32 bit mcu when I and quite happy doing the same job with a £0.70 mcu while saving board space and the grief of having to setup an mcu that has like 10x the peripherals i need and all that.

I could think of some usese for a 100 MHz 8 bit mcu, they might be misuses but if the solution were competitively priced with the correct alternative why not, after all John advocates I should use 32 bit over 8 bit just because it's feasable and he says so  , I'll find you an overkill use for a 100 MHz mcu that probably costs more than the correct part for the job !

[TheDirty]

I don't use 8bit MCU's anymore.  I tend to use MSP430's (16bit) for the simple things and LPC11xx, LPC13xx and LPC17xx for more complex things.

Even though I don't use 8bit MCU's anymore, I can still see why they are used by many.  I use the MSP430 just because it's so simple to use and program.  No worrying about turning on internal peripheral clock modules and such.  Also, development tools and programmers for ARM are locked to code limited versions unless you go to GCC/Eclipse and setting that thing up was way too much work for me.  I use a Olimex JTAG with CrossConnect SWD adapter and Crossworks personal license now, but even that cost is more than what a casual hobbyist is going to want to throw down at the beginning.

[apex]

Some companies even use 4-bit µCs.
Hey, with a 6-pinned ATTiny12 or PIC12Fsomething, I can build a SMPS-controller.
And you want to use 32-bit µPs, just because they have more power.

The controller in my washer has enough calculating power to run windows.
My microwave has an internal ethernet-port.

What are these designers thinking?

The washer is waiting most of the time for the water to heat up.
"My delay loop runs more iterations than yours!!!"
I could build a washing machine with an ATTiny13 (or if program space runs out, with an ATTiny25 /45 /85).
There have been mechanical microwaves.

Why does everyone want more POWER?

Low-power is cheaper, easier to use and more environment-friendly.

If I use an LPC something on my board, I have to use at least two layers.
If I sit down a while thinking and then use a small microcontroller and an more intelligent program, I can use a single-sided board.

Look at what you can do with Arduinos.

I don't need a clock that can run Crysis. It should just display the time!!!

Which company are you working for, john? LPC?

apex

[Psi]

perhaps we should start a new thread
"Why is everyone using 32bit mcus when an 8bit would do the job"

Then we can all argue the opposite 

[Jon Chandler]

Slightly aside, on another forum that shall remain nameless, the "experts" always recommend to newbies that they start programming with a PIC16F628A or maybe a PIC18F1320 if they're radicals.  Why start with a micro with limited port pins and memory?  An 18F2520 or the new 18F25K22 has plenty of memory and port pins or even go to a 40 pin package with an 18F4520.  Spend a buck or two more at the start so that you're not handicapped by memory or port pins right from the start.

[Alex]

I started with the 18F452, now 4520 several years ago.

Microchip targeted this MCU to universities and are therefore offering more than the average level of documenation for this MCU.

[apex]

If you don't have the hardware power to make something, you have to think.
That is the secret behind all the hacks.
You can do something fast by using really big tools.
Or you can do something cheap by thinking a bit.

I won't mind if you use a 32-bit MCU for really really hard things since I'm really lazy to.
But some applications are like using an arduino to blink an led, while you could do it with an 555 timer.

Somewhere in the hackaday comments I found this one:
"What price would I get if I made an Arduino out of 555 timers and the make it blink an led?"

apex

[Ferroto]

And I'm a big proponent of slapping a small $6 FPGA on every design as well,
and that gives me the ultimate flexibility to decide what to do in hardware and
what to do in software.  But you do have to climb the VHDL/Verilog learning
curve.  But none if this is beyond the capability of a hobbyist.

Scott

Heh try explaining to some MBA manager why you choose a $6 FPGA for a project where a $0.75 microcontroller would be antiquate for the job.

Now say for example 50,000 units were produced. Your decision to use a $6 FPGA over a $0.75 8-bit MCU just cost the company $262,500.

At this point the MBA manager will come to the realization that it would be more cost effective to fire you and hire someone who possesses knowledge on a more diverse range of components. and they will do it because MBA managers are cold minded robots that view the efficiency of the company as paramount and everything else a means to that end.

Dave did a blog awhile back about the whole atmel vs avr issue where he stressed the importance of keeping your options open with regards to components.

[Alex]

No wonder engineers that understand the business concepts wrapped around a product are highly sought after; they are the ones in the best position to take, and justify, such design decisions.

[saturation]

There's no reason to build something that can cost less,  if the designer knows other ways of doing so.  All things being equal in a product, price becomes the only issue.

Having just one skill in one type of uC makes one dependent on the manufacturer.  What if the project deadlines require supplies of chips that are not available for one uC but plenty from another?

Flexibility is key, and the more you know and can use, the more valued you are.

[Mechatrommer]

engineers have to comply to company's vision, quality or cost. whether they like it or not.

[Simon]

infact I think many engineers never get to do it their way due to "costs"

[Alex]

Just make sure you mention the word 'Roadmap' in review meetings 

[Simon]

Just make sure you mention the word 'Roadmap' in review meetings 

yees and moving forward, or is it taking this forward..... and all the other office jargon. Hearing some poeple makes me sick, i need to get out before it's too late 

[apex]

Why would you want to replace an ATMEGA32 oder 128?
It is just the more of pins you have, compared to an ATTiny13 (and some bonus functionality).
You don't need external program memory.
You don't need external ram.
You don't need two or three voltages.
You don't need a 4-layer board.

If you just want to build a keyboard (for the PC, not the instrument) and it's not highest-end, you could use an ATMEGA with V-USB.
No struggeling finding board space for all the external components.

A microcontroller is a bit like a standalone platform.
A microprocessor, like an ARM, is part of a powerful system.

It's right, you don't always need microcontrollers.
For example, I don't know why ATMEL made the AT32UC3 series of 32-bit microcontrollers AND the ATSAM series of 32-bit ARMs.
You could also argue about the ATXMEGA, but they are a different field.

But if you put some though in it, you'll find most problems on earth are quite easy to solve.
It just depends on the way and the possibilities if you succed.
For example, let's say, the lamp example further above, I just would use a 555 or 7555.
No problem with foil caps and good resistors.

But for calculating the flight curve of a wing that breaks off an airplane, you'd need power.
And you'd also need power to calculate how to stabilize the plane.
This is, where I'd use an ARM.

Its not that I don't like ARMs.
I love them!
I've used them and will use them again.
But just think of the "THE RIGHT TOOL FOR THE JOB"-Video!

apex

[TheDirty]

^ I'm not certain what ARM chips you are talking about, Cortex-M3 and M0 don't need any  of those things you mentioned.  Any ARM's we design with, even up to ARM7, and ARM9 are still microcontrollers, not microprocessors.  Something like an LPC1xxx series is actually a pretty modest microcontroller.

[House91320]

because it is stupid to us a arm cortex m3 to flip a bit