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HC(S)12 in the field...

Question asked by puppetmaster on Mar 7, 2013
Latest reply on Mar 12, 2013 by Radek Sestak

Hi,

 

it's not really a technical question, but I hope that's OK. I work as an embedded systems software engineer developing firmware for automotive sensors.

We are currently developing a new series of sensors based on Freescale S12G64 MCUs; the predecessors were based on a Microchip PIC18F4680 MCU.

 

My colleagues' opinions about all electrical issues are based on his experience with the named Microchip MCU. It's always like "We had issues with this so we found that solution and we're going to use it as it has been proved to be working just fine"... Well, I'm not one who says "throw away all experiences", but he's pretty stiff on that topic. You can forget to tell him that the newer chip might have better characteristics and so forth.

Especially when it comes to electrical noise which is a pretty relevant topic in the automotive field.

And that is mainly the cause for the question here... no one is willing to take some money, populate several prototypes and test the noise characteristics with different MCU clocks (with or without PLL, 4, 8, 16, 24 MHz)... We even got some noise charts from Freescale for this MCU, but no use -> "The results are for their test boards not ours"...

Therefore I'm stuck in the project I'm assigned to with a 8 MHz crystal and I'm not allowed to turn on the PLL which give me a bus clock of 4 MHz (which is 250ns per tick). The main reason for the 4 MHz is that the Microchip had issues with electrical noise while being clocked with 10 MHz (therefore failed some tests), so I get 4 MHz "and we'll pass every automotive noise test just fine".

It might not be the big deal for some, as the 4 MHz S12G still is approx. three times faster than the higher clocked Microchip MCU, but as we have to do a lot of safety checks (like mirror RAM, check RAM during runtime, check CAN, synchronise with second MCU etc..) this is pretty low end[..]

I'm more busy tweaking my OSEK/VDX implementation and communication stack for as less as possible delays than working on safety relevant issues[..]

 

Therefore I wanted to collect some "out-in-the-field experiences" from users of Freescale S12-Variants to get a simple overview of applications and noise characteristics. That's mainly because I CAN'T believe that a simple 24 MHz processor is not capable to pass automotive noise tests. (I was working for BMW and the MCUs I was working on were running with 120 to 180 MHz (depending on the ECU), and they care for electrical noise).

 

I hope some people are willing to share their experiences and I get some nice replies!

Thank you for reading that whole bunch of text!!

 

So here are my questions:

 

What derivative are you using?

In what kind of product(s) do you use the S12-derivative?

Which clocks are you using (with or without PLL) ?

Which field (automotive, aero, medical, consumer) is the target?

Did you pass critical noise tests for the target field? 

Did you have issues with passing those tests and how did you solve them?

If your product is used in the automotive field, did you have some "special issues" with the car voltage transients?!

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