CMX138A CTCSS encoder/decoder IC

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Hello! I´m looking for a CTCSS encoder/decoder IC. I used to use CML´s MX465, but become obsolete years ago and now I´m having problems to find it besides grey market. CML recommends CMX138A. But the interface is this weird C-BUS protocol. I searched and found nothing about interfacing with Atmel or even some C code examples. 

Anyone have suggestions where to look or maybe a suggestion for a friendly CTCSS IC with a most common interface?

Thanks in advance. 

JR

This topic has a solution.

Good Soldering JRGandara

Last Edited: Sat. Mar 14, 2020 - 10:56 AM
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The magic C-BUS looks like plain spi to me.

 

Many micros would be able to do the dtmf reception and encode in software.

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Kartman wrote:
Many micros would be able to do the dtmf reception and encode in software

Used to be a common topic right here back in the day ...

 

A

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gandara wrote:
CMX138A

You mean this  https://www.cmlmicro.com/products/audio-scrambler-and-sub-audio-signalling-processor/  ?

 

Datasheet:  https://www.cmlmicro.com/wp-content/uploads/2017/12/CMX138A_ds.pdf - gives a description of the C-Bus operation:

 

 

 

 

As Kartman says, looks like SPI !

 

EDIT

 

https://www.cmlmicro.com/ask-a-question/

 

EDIT 2

 

So, in fact, should be easier that the MX465 you're already using - which is way more "non-standard" !

 

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Last Edited: Thu. Mar 12, 2020 - 09:00 AM
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Well, I pretend to use more than only DTMF. This IC offers DCS, CTCSS encoding/decoding concurrent, pre and de enphasys and more. Last time I test DTMF decoding by software was a fiasco compared with a hardware IC like MT8870 which have filters and other goods in order to improve sensitivity. My audio signals comes from noise radio sources instead clean signals. 

I don´t understand why not I2C or SPI as interface. C-BUS looks like a odd option. But that the way it is. frown

Good Soldering JRGandara

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Hummm... The datasheet I downloaded don´t have these waveform. Looks like I got a kind of short version. Thanks!!!

Good Soldering JRGandara

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gandara wrote:
I don´t understand why not I2C or SPI as interface

As already noted, it looks pretty much like it is SPI!

 

. C-BUS looks like a odd option.

It just looks like a perfectly standard use of SPI to me - what do you find "odd" about it?

 

It's the previous chip's interface that's "odd" - if anything!

 

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Last Edited: Thu. Mar 12, 2020 - 01:43 PM
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"As already noted, it looks pretty much like it is SPI!"

Awneil, you made and I got your point now. 

Without wanting to abuse such wisdom, could you tell me why if this protocol is SPI, it is called C-BUS? Any royalties or trademark issues?

Good Soldering JRGandara

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Ask CML! They’ve probably got a family of products that use the same interface, so it made sense for them to name their own bus. Note that all spi devices aren’t necessarily the same - there’s plenty of variation.

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gandara wrote:
if this protocol is SPI, it is called C-BUS?

SPI just defines the 4 wires and how raw bits are transferred over it.

 

C-BUS is the higher-level protocol which gives meaning to those bits in the context of this chip.

 

It's just like a UART simply transfers bytes; then you add higher-level protocols to give meaning to those bytes - eg, XMODEM, AT Commands, etc

 

https://en.wikipedia.org/wiki/OSI_model

 

Any royalties or trademark issues?

As Kartman says, you'd have to ask CML that one.

 

Have you asked them if they have any code examples?

 

 

Top Tips:

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  3. Wrong baud rate is usually due to not running at the speed you thought; check by blinking a LED to see if you get the speed you expected
  4. Difference between a crystal, and a crystal oscillatorhttps://www.avrfreaks.net/comment...
  5. When your question is resolved, mark the solution: https://www.avrfreaks.net/comment...
  6. Beginner's "Getting Started" tips: https://www.avrfreaks.net/comment...
This reply has been marked as the solution. 
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Thank you all for the answers.

CML answered today sending me these two pdf files. Those explanation will help me to go ahead with the tests. This IC is almost perfect for what I need. Could be better if I could use the RX and TX function concurrent since in my application I will need both working at the same time. The block diagram looks like there is two separated circuits but they are not. I will have to use two ICs. 

JR

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Good Soldering JRGandara

Last Edited: Sat. Mar 14, 2020 - 03:41 AM
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gandara wrote:
CML answered today

Why does contacting the manufacturer always seem to be the last thing people think of?

 

frown

 

Anyhow, glad it's resolved the issue - now please see Tip #5 (in my signature)

Top Tips:

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  2. "Garbage" characters on a serial terminal are (almost?) invariably due to wrong baud rate - see: https://learn.sparkfun.com/tutorials/serial-communication
  3. Wrong baud rate is usually due to not running at the speed you thought; check by blinking a LED to see if you get the speed you expected
  4. Difference between a crystal, and a crystal oscillatorhttps://www.avrfreaks.net/comment...
  5. When your question is resolved, mark the solution: https://www.avrfreaks.net/comment...
  6. Beginner's "Getting Started" tips: https://www.avrfreaks.net/comment...
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gandara wrote:
This IC offers DCS, CTCSS encoding/decoding concurrent, pre and de enphasys and more.

 

Some used Basic-stamp for CTCSS in Amateur Magazine as option.

 

Since already with CML then

awneil wrote:
Have you asked them if they have any code examples?

Yes,They will response.Here in my country they had office,unfortunedly the price of CML chips were sky rocket.

 

Probably there was at CML databook,will look.

 

JSB 

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Perhaps because not all people are experienced or smart like you?

I do my best to avoid asking questions on this forum. The result most of the time comes full of ironies and mocking. I´m sure these smart people do that in order to avoid too much dumb questions. But I´m not sure if this work, since dumb people will always do dumb things anyway. But this pleasure for irony must please those experts. 

Of course I asked CML! My contact person was off the office and the contact he passed in his e-mail account was off too! Since I intent to work in this matter this weekend, I give a try here. 

Well, I hope someone else can benefit from this conversation and get good info and documents without having to dare to ask dumb questions. 

JR

Good Soldering JRGandara

Last Edited: Sat. Mar 14, 2020 - 11:20 AM
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I used to use the MX465 but CML do not sale anymore. You can find plenty in Aliexpress but they are grey market. See this video to learn how they always have out of the market ICs or cheap price for any actual IC:

Fake Chips?

Do you know any other option besides CML for those CTCSS audio processing ICs?

JR

 

Good Soldering JRGandara

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The problems with fake chips is known and is common. It is incredible the lengths people will go to in order to make a couple of dollars.

CTCSS is not used with the latest two-way radios as they use digital protocols. Therefore there is not much of a market for the chips. CML still make them, but you pay a premium. As I mentioned in #2, nowadays the microcontrollers are powerful enough to do CTCSS encode/decode in software. A bit of Googling will find you examples of this. I dare say for the price of the CML chip you can buy a very powerful microcontroller.

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The majority of digital radios today also works in analog and come with CTCSS. Still the majority of repeaters in the world are analog. I´m amazed to still sell well an analog controller made back in 2002. But sure is niche market today. I already did a CTCSS decoder in software, but the glue you have to have for filtering and other goods normally came to cost of space and even price. This CM138A do much more than CTCSS, as DE-emphases, mute, volume digital control, filters and more. In my specific case is not worthy do in software.

The problem with these grey market chips is that even traditional local distributors are being fooled (no not) by these sellers.  

Good Soldering JRGandara

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gandara wrote:
The problem with these grey market chips is that even traditional local distributors are being fooled (no not) by these sellers.  

 

Yes,Did you had their databook ?

 

Where do you lived ?

If you want,given to you.The CML little bit expensive but good chips

 

Jeck

 

.

Last Edited: Mon. Mar 16, 2020 - 10:35 AM