CMU200 remote control over usb to rs232

[crossrulz]

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Jeff·Þ·Bohrer wrote:

Essentially that R&S COM interface expects RS-232 to be +/- 12V but is +/- 5V compliant and the converter you have provides 0-3.3V logic.  So, it sees "Maybe" a logic 1 but never a logic 0  I'm betting that the device never even goes into remote.

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This is not always true for adapters with Prolific chipsets.  I have several TU-S9 (which does use the Prolific chipset, $10 on Amazon last I looked) and never had a problem with them.  And they do put out true RS-232 levels.

I actually have the opposite problem right now, I have an instrument that wants TTL level UART, so I need an adapter to go from RS-232 to TTL.  Luckily, I have a chip that I have been using for other applications that will do this for me.

[crossrulz]

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@JÞB wrote:

Ah, the Prolific chip set!

It won't work without an external level shifter.

FTDI has some options with integrated level shifters to operate at voltages that emulate a RS 232 interface

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Another thing I should mention, FTDI chips also only put out TTL or LVTTL level UART signals.  They just put level shifters inside of their full products.  Prolific does not make end products, so you have to watch the specifications of the manufacturers who use their chips.

Spoiler

I have been looking into this way too much lately since I want to use one of these chips for a test system.

So the real lesson here: check your voltage levels with an oscilloscope when you have a new USB-RS232 adapter (most that I have seen do not state the voltage levels anywhere).

[JÞB]

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@aAmecareth wrote:

Thank you so much !!

I could have searched a really long time before figuring it out.

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Oh... I KNOW!  All too well. 

[aAmecareth]

Hey

I finally managed to get it working thanks to your help.

My new problem is that very few remote commands are working on my CMU, right now the CMU won't process any request regarding the RFANalyzer.

Any ideas?