[time-nuts] Follow-up question re: microcontroller families

Sun May 26 13:19:19 EDT 2013

Hi

On May 26, 2013, at 11:21 AM, Herbert Poetzl <herbert at 13thfloor.at> wrote:

> On Sun, May 26, 2013 at 07:46:38AM -0400, Bob Camp wrote:
>> Hi
> 
>> On May 25, 2013, at 11:26 PM, Herbert Poetzl <herbert at 13thfloor.at> wrote:
> 
>>> On Sat, May 25, 2013 at 09:26:02PM -0400, Bob Camp wrote:
>>>> Hi
> 
>>>> I realize this is a bit like water torture - sorry about that.
> 
>>>> If I go to Microchip Direct and ask for a PIC 18F with two
>>>> UARTS and two A/D's I get the PIC18F86J72 and PIC 18F87J72.
>>>> To me the second one is the obvious winner. It's got twice
>>>> the flash for next to nothing more money. 1-25 piece price is
>>>> $6.04.
> 
>>>> Same search, 1 A/D, 4 UARTS, lowest cost this time. PIC18F65J94
>>>> is the winner. Lowest price package is $3.30 in 1-25 pieces.
> 
>>> 4 UARTS are untypical for PICs and result in higher price
>>> as the device usually has more pins (which makes them more
>>> expensive)
> 
>> The ARM that the thread was looking at was a 6 UART / 4 A/D
>> part. Thus the "load up the UARTS". Also the starting point 
>> for all this did involve serial i/o.
> 
> I have no idea for what 'home' project you would make
> good use of 6 UARTs,

One port to grab pps sawtooth data from the LEA-6T GPS
One port to steer the FE-5680 rubidium
One port to the console / logger / debug
One port to drive pps into NTP on the PC
One port to grab data out of the 53131 monitor counter
One spare

> but please don't get me wrong,
> I'm using a lot of ARM/MIPS microcontrollers and
> devices here, and I appreciate that they got really
> cheap over the years.
> 
> But for many applications, the inevitable overhead
> (power, heat, external components, OS, etc) simply 
> eliminates the gain of having a better/faster CPU.

The ARM part I mentioned earlier runs much the same way as a PIC. You can run on it's internal oscillator, add a crystal (or two), or dump a clock oscillator into it. Past that it's stand alone unless you implement USB or Ethernet. In both cases you add a connector and a few bits here and there. Current wise it pulls about 90 mils at 1.8 to 3.6 volts running at 150 MHz. You can throttle it back so it runs on a few microamps if you wish. Like the PIC it's perfectly happy with an unregulated supply, within limits. The full trace and debug connector is 20 pins, a simple programing connector with limited debug is 10 pins. All this is in no way unique to that part, All of the M0's and M4's I've seen are similar. 

The RTOS is free and the lightweight version has a very cute configuration wizard. It's literally a "zero to up and running in less than a day" sort of thing. Since it adds things like interrupt driven buffered serial I/O it's quite a bit faster than writing the code from scratch. If you head off into USB plus Ethernet, an OS is pretty much a necessary evil. The specific RTOS is Freescale specific. Other vendors toss in their favorite OS (or not…). My guess is that those in the "not" category soon will start supplying one, simply to keep up. My belief is that for a one off home project, the OS with all the wizard configured drivers is very much the way to go. Your time would have to be worth very little to make it worth writing all that code from scratch for a one up. 

The free tool chain is Eclipse / GCC. You can love it or hate it (or both at once). The ARM toolchain is nontrivially expensive with debug. It's certainly "better", but to my mind out of range for a home only setup. 

What is *very* true is that soldering a bazillion pins when you only need a dozen is a bit crazy. The M0 parts get down to sub 32 pin packages at sub $1 sort of prices. You loose the Ethernet, and probably USB. You do keep some UARTS and A/D's even on the smaller parts. 32 pins is not a lot, so getting at everything at once will be a chore.

Lots of choices at many price points. 

Bob

> 
> Sometimes I end up using a 6 or 8 pin PIC with only
> a few lines of code to to solve complex problems where
> a (F)PGA/CPLD design would be a lot of work and a 
> 16/32bit microcontroller simply overkill.
> 
> As always, YMMV, best,
> Herbert
> 
>>>> Are those some *very* arbitrary choices - you bet they are.
>>>> They are random picks, and were not optimized to show any
>>>> particular thing. Only to target an application that had some
>>>> serial i/o and a bit of A/D involvement.
> 
>>>> Bottom line - not all PIC's are $1. once you start adding
>>>> peripherals. For $6 over in ARM land, you can get a lot of
>>>> chip. To be fair, my experience has been that you can do better
>>>> in the PIC24 line once you start adding stuff. Searching the
>>>> PIC24's is hard enough that my brief search tonight did not
>>>> show up a lower cost part.
> 
>>> PIC24F04KA200 1 UART, 10 ADC, XLP, 1.38 USD (1.05 USD @1k)
>>> PIC24EP32GP202 2 UART, 6 ADC, 2.76 USD (1.86 USD @1k)
> 
>> I knew they had to be there. Again suggesting that the PIC24's probably are a better starting point these days.
> 
> 
>>> One (dis)advantage of the Microchip PICs is that there
>>> are so many different families and parts.
> 
>> Indeed
> 
>> Bob
> 
> 
>>> best,
>>> Herbert
> 
>>>> Bob
> 
>>>> On May 25, 2013, at 9:05 PM, Bob Camp <lists at rtty.us> wrote:
> 
>>>>> Hi
> 
>>>>> I just realized the "buy direct" button on that page requires a login. The single piece direct price is $9.70. First price break is at 25 pieces (to $8.95).
> 
>>>>> Bob
> 
>>>>> On May 25, 2013, at 8:56 PM, Bob Camp <lists at rtty.us> wrote:
> 
>>>>>> Hi
> 
>>>>>> It's one of the Freescale K60's they have them in several speeds and packages. Others have similar parts.
> 
>>>>>> http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=K60_120&nodeId=01624698C9DE2DDDAF&tab=Buy_Parametric_Tab&fromSearch=false
> 
>>>>>> hopefully shows the family information
> 
>>>>>> The first part on the list is the MK60FN1M0VLQ12 for 8% more money you can get the 150 MHz core rather than the 120 MHz core version. Both have enough pins that you can get at a lot of the peripherals at once. Both have enough pins that they are not a lot of fun to solder by hand. Of course their BGA cousins are even less hand solder friendly….
> 
>>>>>> Bob
> 
> 
>>>>>> On May 25, 2013, at 6:48 PM, Graham / KE9H <timenut at austin.rr.com> wrote:
> 
>>>>>>> On 5/25/2013 3:40 PM, Bob Camp wrote:
>>>>>>>> You can get a part with 1MB of flash, 128KB of ram, 6 UARTS, 4 16 bit A/D's, 10/100 Ethernet, USB, and a bunch of other stuff for less than $10. Drop this and that, go to half the flash, and yup, the price is 1/2. Comes with a free toolchain and two very capable free versions of RTOS.
> 
> 
>>>>>>> Bob:
> 
>>>>>>> I was wondering which manufacturer/part you were referring to.
> 
>>>>>>> Thanks,
>>>>>>> --- Graham
> 
>>>>>>> ==
> 
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