Thread: How to decode a protocol like SPI by using MSO9104A?

Hi, I am using MSO9104A. I want to decode a non-standard SPI protocol (like SPI, but not). There are MISO, MOSI and CLK (no Chip Select).

I tried 14-days SPI option trail. My settings are as follow:
4 wire SPI;
MISO - Channel 2
MOSI - Channel 3
CLK - Channel 1
Chip Select - Channel 4 (I tried ground it and set "active low"; also I tried give it 5V and set "active high")
Auto Setup;
Trigger: Serial: Channel 3 (I want to select CLK channel as Trigger, but the only options are channel MISO and MOSI.)
Trigger (another try): Edge: Channel 1 - CLK; falling;

others are default.

I always got the message - "can't decode. not enough edge."

I just need to figure out how to decode MOSI and MOSI based on the CLK.

For example, I can decode some by hand. When CLK is active, count the level of MISO such as "high low high low low low low low" (101010000)bin=(A0)hex. Then, convert 8 bit binary value to hex.

How to use agilent oscilloscope to do this?

Thanks a lot.

My device doesn't have chip select. There are a master device and a salve device. The electronic connections between them are just MISO, MOSI, CLK, VDD and GND. I tried use VDD as chip select(active high). It always says "can't perform serial decode; not enough edges". I have a couple times that the decode displays, but the result is wrong (the decode is not referring to the clock).

I am seeking a efficient and reliable way to decode the serial signal that is non-standard SPI.

I tried 2 wire SPI, but I don't know how to set the clock timeout and word size. The default setting doesn't work(still cannot decode; not enough edges). When I change clock timeout to 13 us that is close to the period of clock and word size=8 (my serial communication is 8 bit), it seems shows the correct decode. However, how can I run two 2-wire-SPI decode to compare the MISO and MOSI?

Thanks a lot. You did awesome troubleshooting.

Edited by: jenaflex on Jun 21, 2012 2:53 PM

Check out this video I made of doing exactly this:

http://www.youtube.com/watch?v=jiK6P7f1frU&sns=em

The error message you are getting is either as Al said, where the signals or thresholds are not set properly, or often you simply don't have enough data on screen; try going to a longer timebase.

As I said in my post of 6/21, you need to have the newest SW, or pretty close to it. The current version is 3.50.something. It is available here: http://www.agilent.com/find/scope-apps-sw Once you have done that, you will be able to follow Kevin's instructions to get the decode. The update will take an hour or two, since you are so far behind. You will have to run a user calibration on it after doing the update.

First, before you load the latest firmware, you should connect it to the internet, and run Microsoft Update as many times as necessary, if you haven't done that in a while. Make sure you get all of the latest .NET patches. Remember, besides being a scope, it's a PC. If you don't have antivirus SW, you should install some. I recommend Microsoft Security Essentials (MSE). It's free and relatively low-load.


You don't have a "true" 4-wire SPI, so as I said earlier, using the 4 wire decode doesn't and won't work. You need to treat it like 2 2-wire SPI links, that happen to share a clock. to do that, you need the newest SW, and you'll use 2 probes on the clock.


In some cases, yes. While you are installing the newest SW, read the "ReadMe" document, that talks about the changes that have been added since you last updated. Then, look in the "Script and Programs" section for some pointers, including examples. If you post there, others will get the benefit of seeing the answers.

Al