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How do I use the serial decoder function on the MDO3000?

Question :

How do I use the serial decoder function on the MDO3000?

Answer :

Hello and welcome to Tektronix, today I’m going to demonstrate the serial decoder capabilities of the MDO3000 series mixed domain oscilloscope.

The MDO3000 has the ability to decode bus data into binary, hexadecimal, decimal, or ASCII values depending on the protocol. It will separate the decoded data into address, control, data, and clock information. In addition to decoding the signals, the MDO3000 can trigger on decoded content, including start of packet, specific addresses or data, unique identifiers, and more.

For this demo I’m looking at an I2C bus, with channel 1 acquiring the I2C clock and channel 2 acquiring the I2C data. I’ll change my record length to 1M points in order to reach the timing resolution necessary to decode the bus.

I can change my record length by pressing the Acquire button, pressing the Record Length softkey, and using the multipurpose knob A to change the record length. Let’s also change the horizontal scale to acquire more data and capture a single acquisition by pressing the Single button. To bring up the bus decode function, press the B1 button, press the Bus B1 softkey, and use the multipurpose knob A to select I2C. Press the Define Inputs softkey and make sure that the channels are assigned to the correct inputs.

Press the Thresholds softkey and set the thresholds using the multipurpose knob A for channel 1 and multipurpose knob B for channel 2. The threshold levels tell the scope the level above which should be decoded as a data 1 and below which is a data 0. You can now see the decoded bus values show up on the purple bus line in the middle of the screen. Zoom in on the decoded values using the inner Wave inspector knob and pan around using the outer wave inspector knob. You can see the Address bits bordered in yellow and the data bits bordered in blue. You’ll also notice that the start of packet is marked by a green bracket and the end of packet is marked by a red bracket.

To change the way the data is decoded, press the Bus Display softkey and toggle between Hexadecimal and binary with their respective softkeys. You can also use the Event Table to view all the decoded values in tabular form. Select the Event Table softkey and then select the Event Table On/Off button to toggle the Event Table. The multipurpose knob A can be used to scroll through and select events, all of which are time correlated, and the Event Table can be exported as a .csv file if an external drive is mounted.

To trigger on decoded information, go to the trigger menu, press the Type softkey and scroll down to Bus using multipurpose knob A. Press the Trigger On softkey and select Address using multipurpose knob A. Set the address value by pressing the Address softkey at the bottom of the screen, select the Address softkey on the side of the screen, and use multipurpose knob A to change the cursor position and use multipurpose knob B to change the value. I’m going to trigger when the scope sees an address of 50 hex. I can select the direction to write, read, or both using the Direction softkey. Now, whenever I press the Single acquisition button, the scope will trigger when it finds a 50 hex address. Notice the orange trigger arrow is right above the address.

You can also search for different decoded values within your acquisition. In this case, I want to see all the places that the bus sends a 50 hex address. Press the Search button, press the Search softkey, select the Search On/Off softkey to turn it on, and press the coppy Trigger Settings to Search softkey. You can use the Wave inspector arrows to jump between instances of the search event. Much like the Event Table, you can use the Mark Table to view all the instances of the search event in tabular form. Press the -more- 1 of 2 softkey and press the Mark Table softkey to turn on the Mark Table

Instead of manually counting clocks, determining if a bit is a 1 or a 0, combining bits into bytes, and compiling all the information yourself, the MDO3000 will do it all for you. This is just one of the many useful features the MDO3000 brings to the test and measurement table.

This FAQ Applies to:

Product Series: MDO3000 Mixed Domain Oscilloscope


FAQ ID 69296

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