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Base frequency of Märklin digital
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Offline perz  
#1 Posted : 08 September 2004 01:17:32(UTC)
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perz

Sweden   
Joined: 12/01/2002(UTC)
Posts: 2,578
Location: Sweden
This is a continuation of a topic I started about a year ago, but the old topic is locked and archived now.

The question was: Is the base frequency of Märklin digital 38.4 kHz or 40.0 kHz ? The conclusion then was that it was probably 38.4 kHz.

Now, I have finally had the chance to measure the output of a 6021, and I can therefore see that our conclusion was wrong. The base frequency is 40 kHz in a 6021.

The precision in my measurement is approximately +/-0.5 kHz so I can not say for sure whether it is exactly 40 kHz or just close.

Whether it is different in e.g. Delta, 6020 or Märklin Systems I can't tell.
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Offline Tamrac  
#2 Posted : 08 September 2004 05:23:33(UTC)
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Tamrac


Joined: 08/11/2003(UTC)
Posts: 197
Location: Frenchtown, New Jersey USA
I was not quite a member of the forum a year ago, but your reason for gaining this knowledge is what?
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Offline Gregor  
#3 Posted : 08 September 2004 10:44:21(UTC)
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Gregor

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Joined: 17/04/2003(UTC)
Posts: 997
Location: Netherlands
Hi Tamrac,

Some people with knowledge of electronics build their own control unit and boosters. They have to know the nature and philosophy of the digital signal. Especially now that the current protocol is being enhanced with the extra signal for Marklin Systems, they want to find out if they have to throw out their existing equipment, or just upgrade it.

Best regards,
Gregor
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Offline perz  
#4 Posted : 08 September 2004 12:35:17(UTC)
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perz

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Joined: 12/01/2002(UTC)
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Location: Sweden
Yes, this is interesting to know if you are building your own control equipment and/or your own decoders.

It is obviously possible to use 38.4 kHz as base frequency in your do-it-yourself equipment, but using the correct nominal frequency will probably give you the best operating tolerances and the best reliability.

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Offline perz  
#5 Posted : 08 September 2004 13:34:13(UTC)
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perz

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Joined: 12/01/2002(UTC)
Posts: 2,578
Location: Sweden
Background information for those who haven't digged into the details of the Märklin Digital protocol:

The Märklin Digital protocol(also called Märklin/Motorola or Motorola protocol) sends digital 1:s as 7 time units of positive voltage followed by 1 time unit of negative voltage. Digital 0:s are sent as 1 time unit of positive voltage followed by 7 time units of negative voltage. Thus 8 time units are needed for one bit. The base frequency gives the length of one time unit. Each data packet consists of 18 bits and the packet is sent twice with a well defined pause (= negative voltage) to allow error checking.

The two references for the Märklin Digital protocol are Rutger Friberg and Andrea Scorzoni. Rutger Friberg says the base frequency is 40 MHz, Andrea Scorzoni says 38.4 kHz. Now it seems Rutger Friberg had the correct figure.

The base frequency discussed here is for the loco commands. Accessory commands use the double frequency.
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Offline nico van zon  
#6 Posted : 08 September 2004 17:58:45(UTC)
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nico van zon


Joined: 25/07/2004(UTC)
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According to the Edits book the basic pulselength is 26 microsec.
The reciproke value of this gives 38.46kHz
Also interesting is this webpage: http://people.zeelandnet.../zondervan/digispan.html
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Offline perz  
#7 Posted : 08 September 2004 18:48:18(UTC)
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perz

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Joined: 12/01/2002(UTC)
Posts: 2,578
Location: Sweden
[url]According to the Edits book the basic pulselength is 26 microsec.
[/url]

Either they are wrong, or the precision of my measurement is too low. I will try to double-check it with more accurate equipment.
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Offline nico van zon  
#8 Posted : 08 September 2004 19:31:32(UTC)
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nico van zon


Joined: 25/07/2004(UTC)
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Perz, just curious: why do you need to know this so precise?
You only must discriminate between pulselengts op 13, 26, 91 and 182 uS.
These values are far enough apart to see the difference, even with a low accuracy measurement.
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Offline perz  
#9 Posted : 11 September 2004 20:38:14(UTC)
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perz

Sweden   
Joined: 12/01/2002(UTC)
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Location: Sweden
As I have mentioned in another post:

Mobile Station and 6021 use different base frequencies! Probably the Mobile Station uses 38.4 kHz and the 6021 uses 40 kHz, but my measurement precision is still only around +/- 0.5 kHz so I can't say exactly.
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Base frequency of Märklin digital (Digital)
by perz 08/10/2003 12:19:08(UTC)
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