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YanNaingAye
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PostSubject: real time communication   Wed Nov 08, 2006 8:10 am

I've got to design a system with real time communication. (soft, loss tolerance~0, delay<1 s, jitter is not importent-as long as delay is within limit, message oriented). I found freescale's 68HC908GZ16 mcu with built in CAN controller is cheap but the transceiver chip MC33388 can have max 32 nodes only. Is it possible to use that MCU with philip's transceiver PCA82C250 that can connect more than 110 nodes in a segment? ( I have no experience in Freescale).
Can some LIN nodes and some CAN nodes be put in the same segment of bus? I don't know LIN but I heard it is subnetwork of CAN.
Any idea is appreciated.
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bobowaimg
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PostSubject: Re: real time communication   Thu Nov 09, 2006 7:34 am

btw, let me know the differenences bet 68HC11 and 12 series and urs...?
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YanNaingAye
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PostSubject: Re: real time communication   Thu Nov 09, 2006 9:55 am

HC11 is legacy 8 bit and HC12 is 16 bits. Pls check
http://www.freescale.com/webapp/sps/site/overview.jsp?nodeId=016246863636225542&tid=t16dr

The chosen one is
http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=68HC908GZ16

Thanks for your attention.
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bobowaimg
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PostSubject: Re: real time communication   Thu Nov 09, 2006 12:10 pm

YanNaingAye wrote:
HC11 is legacy 8 bit and HC12 is 16 bits. Pls check
http://www.freescale.com/webapp/sps/site/overview.jsp?nodeId=016246863636225542&tid=t16dr

The chosen one is
http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=68HC908GZ16

Thanks for your attention.

k... cos i have one site for HC11 applications and projects... hope u may find helpfull http://www.evbplus.com/
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ZawMinHt
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PostSubject: Re: real time communication   Thu Nov 09, 2006 3:30 pm

Hi Yan Naing Aye,

I have never used the line drivers you described. But I believe ** you can use both of them** with HC908 micro although they may not be drop-in equivalents. Since they both are line drivers, their main functionality is to pull-up or pull-down the electrical interface levels. CAN is in fact a variant of RS-485. It uses a balanced differential lines ( two wires ) . Because of their differential nature, they have high CMRR common-mode rejection ratio and high SNR signal to noise ratio. In addition , ground potential difference is not a problem any more. Although theoretically only two wires is enough for communication, a ground loop is usually applied. It is amazing , sometimes even when a data wire is broken , it still works. One example of differential interface is USB. USB has four pins, +5V,GND, and D+,D- . Untwisted pair can do the job for many cases. But twisted pair cables are prefered because of they noise immunity and less electromagnetic radiation although electromagnetic radiation can be reduced by controlling slew rates of line drivers.

I don't think you can use both LIN and CAN on the same physical network. Since they have quite different electrical level requirement and LIN is one wire interface similar RS-232. You cannot use LIN for high speed and long distance. Not quite good for noisy environments because of their lack of immunity to both common-mode and differential-mode noise signals. Although you may be able to put LIN and CAN together by pulling the electrical signals to fit for both it would lose all the goodness of CAN. One more thing is LIN will have much higher output level requirement on "driver" side than on "receiver" side.
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YanNaingAye
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PostSubject: Thanks   Fri Nov 10, 2006 9:42 am

HI bo bo,
Thanks for your site!
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YanNaingAye
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PostSubject: Thanks   Fri Nov 10, 2006 10:13 am

Hi Htut Gyi,
Thanks for your detail explanation! I think I have to use CAN for all nodes although MCU with LIN(Slave) are very cheap and small. Crying or Very sad I need to communicate about thousand of sensors with the distance of about 5km. Seems LIN is not suitable becasue of cabling constraint (two layers is not preferred). Thanks for sharing knowledge.
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