Forums

LM555 in Automotive application

Started by K.P.Venu December 14, 2002
Hi All,
I want to add a 100Hz external reference clock to my
HC12 hardware (D60A).I am planning to use SG555 or
LM555 as a 100Hz square wave generator.
Is there anybody using LM555 in automotive
application?
Is it advicable to use this chip in automotive
environment?
Please advice.
Thanks and Regards
Venu __________________________________________________




Venu:
Have you considered generating your 100 Hz using one of the timer output
compares? That would reduce costs, and consume only 1 I/O.

Regards--

607-656-2597 -----Original Message-----
From: K.P.Venu [mailto:]
Sent: Saturday, December 14, 2002 12:03 AM
To:
Subject: [68HC12] LM555 in Automotive application Hi All,
I want to add a 100Hz external reference clock to my
HC12 hardware (D60A).I am planning to use SG555 or
LM555 as a 100Hz square wave generator.
Is there anybody using LM555 in automotive
application?
Is it advicable to use this chip in automotive
environment?
Please advice.
Thanks and Regards
Venu __________________________________________________

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Hi Dave,
Actually I want to generate an external reference
clock to monitor some internal timings.

The ECT module already filled with 6 capture inputs
and 2 compare ouputs (for two different timings).
I am also using the modulus down counter as an another
timer.
Venu

--- Kellogg Dave <> wrote:
> Venu:
> Have you considered generating your 100 Hz using one
> of the timer output
> compares? That would reduce costs, and consume only
> 1 I/O.
>
> Regards--
>
> 607-656-2597 > Hi All,
> I want to add a 100Hz external reference clock to my
> HC12 hardware (D60A).I am planning to use SG555 or
> LM555 as a 100Hz square wave generator.
> Is there anybody using LM555 in automotive
> application?
> Is it advicable to use this chip in automotive
> environment?
> Please advice.
> Thanks and Regards
> Venu


__________________________________________________



Venu:
Sounds like high utilization.

Have you considered a programmable divider on e-clock, such as the 47HC7292?
Divides from 2**2 to 2**31. Just a thought. Of course, it sounds as if you
ready *don't* want anything derived from the MCU itself, if your intent is
to cross-check the MCU. 607-656-2597 -----Original Message-----
From: K.P.Venu [mailto:]
Sent: Monday, December 16, 2002 9:43 AM
To:
Subject: RE: [68HC12] LM555 in Automotive application Hi Dave,
Actually I want to generate an external reference
clock to monitor some internal timings.

The ECT module already filled with 6 capture inputs
and 2 compare ouputs (for two different timings).
I am also using the modulus down counter as an another
timer.
Venu

--- Kellogg Dave <> wrote:
> Venu:
> Have you considered generating your 100 Hz using one
> of the timer output
> compares? That would reduce costs, and consume only
> 1 I/O.
>
> Regards--
>
> 607-656-2597 > Hi All,
> I want to add a 100Hz external reference clock to my
> HC12 hardware (D60A).I am planning to use SG555 or
> LM555 as a 100Hz square wave generator.
> Is there anybody using LM555 in automotive
> application?
> Is it advicable to use this chip in automotive
> environment?
> Please advice.
> Thanks and Regards
> Venu


__________________________________________________

------------------------ Yahoo! Groups Sponsor ---------------------~--> Get
128 Bit SSL Encryption!
http://us.click.yahoo.com/CBxunD/vN2EAA/xGHJAA/dN_tlB/TM
---------------------------------~->

--------------------
">http://docs.yahoo.com/info/terms/



Yes. It is for a cross-check of MCU timings.

--- Kellogg Dave <> wrote:
> Venu:
> Sounds like high utilization.
>
> Have you considered a programmable divider on
> e-clock, such as the 47HC7292?
> Divides from 2**2 to 2**31. Just a thought. Of
> course, it sounds as if you
> ready *don't* want anything derived from the MCU
> itself, if your intent is
> to cross-check the MCU. > 607-656-2597 > -----Original Message-----
> From: K.P.Venu [mailto:]
> Sent: Monday, December 16, 2002 9:43 AM
> To:
> Subject: RE: [68HC12] LM555 in Automotive
> application > Hi Dave,
> Actually I want to generate an external reference
> clock to monitor some internal timings.
>
> The ECT module already filled with 6 capture inputs
> and 2 compare ouputs (for two different timings).
> I am also using the modulus down counter as an
> another
> timer.
> Venu


__________________________________________________



Venu

I dont like the idea of using the 555 as a freq reference in Automotive, as the
frequency based on the capacitor
value, and the temperature conditions are not good for such an application.
Try connect 32khz crystal to 4060 chip, and use one of its prescale outputs

Benny

---------- Forward Message ----------

To:
From: "K.P.Venu" <>
Date: Mon, 16 Dec 2002 06:42:39 -0800 (PST)
Subject: RE: [68HC12] LM555 in Automotive application

Hi Dave,
Actually I want to generate an external reference
clock to monitor some internal timings.

The ECT module already filled with 6 capture inputs
and 2 compare ouputs (for two different timings).
I am also using the modulus down counter as an another
timer.
Venu

--- Kellogg Dave <> wrote:
> Venu:
> Have you considered generating your 100 Hz using one
> of the timer output
> compares? That would reduce costs, and consume only
> 1 I/O.
>
> Regards--
>
> 607-656-2597 > Hi All,
> I want to add a 100Hz external reference clock to my
> HC12 hardware (D60A).I am planning to use SG555 or
> LM555 as a 100Hz square wave generator.
> Is there anybody using LM555 in automotive
> application?
> Is it advicable to use this chip in automotive
> environment?
> Please advice.
> Thanks and Regards
> Venu


__________________________________________________ --------------------
">http://docs.yahoo.com/info/terms/
---------- End of Forward Message ----------




Thanks Benny, I have the same doubts.
I will try your method.
Venu
--- In , RTS development - Benny Rabin
<benny@r...> wrote:
> Venu
>
> I dont like the idea of using the 555 as a freq reference in
Automotive, as the
> frequency based on the capacitor
> value, and the temperature conditions are not good for such an
application.
> Try connect 32khz crystal to 4060 chip, and use one of its prescale
outputs
>
> Benny


You can build a very simple oscillator with pretty good stability using a
Schmidt input inverter ('HC14) and one resistor and one capacitor as long as
you have a fairly stable supply and decent components.

Another approach would be to use the 'HC4538 Monostable Multivibrator.
These are highly stable devices when used with decent componts.

Bob Smith --- Avoid computer viruses, Practice safe hex ---

-- Specializing in small, cost effective
embedded control systems -- Robert L. (Bob) Smith
Smith Machine Works, Inc.
9900 Lumlay Road
Richmond, VA 23236 804/745-1065
----- Original Message -----
From: <>
To: <>
Sent: Monday, December 16, 2002 10:07 PM
Subject: [68HC12] Re: LM555 in Automotive application > Thanks Benny, I have the same doubts.
> I will try your method.
> Venu
> --- In , RTS development - Benny Rabin
> <benny@r...> wrote:
> > Venu
> >
> > I dont like the idea of using the 555 as a freq reference in
> Automotive, as the
> > frequency based on the capacitor
> > value, and the temperature conditions are not good for such an
> application.
> > Try connect 32khz crystal to 4060 chip, and use one of its prescale
> outputs
> >
> > Benny >
>
> -------------------- >
> ">http://docs.yahoo.com/info/terms/ >




Since the 68HC12 has its own internal timebase,
not sure the purpose of an external timer....??

Unless maybe you're thinking of a kind of external
watchdog timer? So that in the event of a hardware
or software failure of the main MCU, the overall system
would recover? If so, there are various reset generator
chips that include external watchdog timers. Also there
are power supply chips that include both a low voltage
reset, and a watchdog timer.

Best regards,

Kerry Berland

Silicon Engines
2101 Oxford Road
Des Plaines, IL 60018 USA
847-803-6860
Fax 847-803-6870

----- Original Message -----
From: kp_venu <>
To:
Sent: Monday, December 16, 2002 9:07 PM
Subject: [68HC12] Re: LM555 in Automotive application Thanks Benny, I have the same doubts.
I will try your method.
Venu
--- In , RTS development - Benny Rabin
<benny@r...> wrote:
> Venu
>
> I dont like the idea of using the 555 as a freq reference in
Automotive, as the
> frequency based on the capacitor
> value, and the temperature conditions are not good for such an
application.
> Try connect 32khz crystal to 4060 chip, and use one of its prescale
outputs
>
> Benny
--------------------



Thanks Bob Smith and Kerry.
Kerry,
Recently I had a "slow clock" problem in my system.
When I discussed this with Motorola engineer, he said it may due to
crystal startup problem and suggested to check the LIMP-HOME flag
before writing to PLL registers. I have successfully implemented this
(thanks to Darci) and till date no problem has been reported from the
field.

But still I am not able to conclude that it is a crystal problem
because I am using an External Watchdog timer which has a Power-ON
reset delay of 600ms and timeout period of 150ms. I believe this
power-on delay is more than enough to start the oscillation.
I am using a voltage monitor too.(MC33164)

I have added two more things to check the slow clock,
1. External watchdog refreshment time modified to 100ms so that any
slow clock will delay the refresh time and initiate a reset.
2. Monitor Timer0 and MDC occurrence using RTI interrupt for a
predefined time (say 65.535ms).
Above methods are good for detecting slow clock but not smart enough
to detect a faster clock (due to wrong settings of PLL registers). So
I am planning to input a low frequency external reference signal for
counting the clock. This may not be a good idea but I need to do some
quick fix for this problem.

If anybody has any better idea please tell me.

Thanks and Best Regards,
Venu
--- In , "Kerry Berland" <kerry@s...> wrote:
> Since the 68HC12 has its own internal timebase,
> not sure the purpose of an external timer....??
>
> Unless maybe you're thinking of a kind of external
> watchdog timer? So that in the event of a hardware
> or software failure of the main MCU, the overall system
> would recover? If so, there are various reset generator
> chips that include external watchdog timers. Also there
> are power supply chips that include both a low voltage
> reset, and a watchdog timer.
>
> Best regards,
>
> Kerry Berland
> kerry@s...
> Silicon Engines
> 2101 Oxford Road
> Des Plaines, IL 60018 USA
> 847-803-6860
> Fax 847-803-6870