 Joined: 12/01/2002(UTC) Posts: 2,578 Location: Sweden
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I wonder which the correct base frequency for Märklin digital system is ? Rutger Friberg states 40 kHz, but I have seen others stating that it is 38.4 kHz. I use 38.4 kHz in my home-made system, and it works well, but I want to know which frequency that is the really correct one.
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Joined: 19/10/2001(UTC)
Posts: 2,379
Location: Lindome, Sweden
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Perz,
I use A Scorzoni as reference in this matter, as he made thorough measurements. He states 38.4 kbaud. I doubt you will find any official statement from Märklin, both not about nominal value, and not about tolerances either. I also know that Rutger has admitted that there was some error in his original books; I don't remember the nature of it though; possibly it was an error in suggested values for the RC-bridge determing the frequence of the Motorola chips. BTW, I also got the impression that tolerances have been getting smaller over the years; not surprising.
/Lars
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Joined: 12/01/2002(UTC) Posts: 2,578 Location: Sweden
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The frequency is controlled by crystals in both the Control Unit and the modern decoders, so there shouldn't be much variation. It is easy to measure if you have a 6021, but I don't have one.
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Joined: 19/10/2001(UTC)
Posts: 2,379
Location: Lindome, Sweden
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At last we've found a use for a 6021... :-)
Do you doubt then that Andrea is right? He obviously measured on a 6021? And why do you ask?
/Lars
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Joined: 12/01/2002(UTC) Posts: 2,578 Location: Sweden
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Andrea has made the comment "Comment:this is the clock frequency of the old 6020". Should that be interpreted as if 6021 is different? I don't think so but I don't know.
I ask because I have made a simple control HW that allows me to use the PC as a "control unit" without having to go to real-time programming like DDL. That HW is based on a PIC processor. It uses 38400 Hz since it is 4 x 9600 Hz and I run 9600 baud from the PC. The PIC program becomes much simpler that way, and it has worked very well so far.
Now I am planning to build a new version which is a more full blown control unit (except the booster part, I have a separate booster). I will use a much more capable processor and it is not necessary to match the track frequency to the serial communication baud rate any longer. Of course I want to be as close as possible to the correct nominal frequency to get the best possible reliability.
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Joined: 19/10/2003(UTC)
Posts: 2
Location: Belfeld,
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Hi Perz,
As i've developed my own digital system i can asure you the base frequence is 38400 Baud. Or a 26us bitrate. For function decoders like k83,k84 the frequence is twice as high: 76800 baud.
I generate the MM format using a PIC processor at 20Mhz connected directly to the printer port of my laptop. (And my own software!)
Regards,
Fred |
Model Railroad.. more than just a hobby.. |
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