Take a look at our
ThinkPads.com HOME PAGE
For those who might want to contribute to the blog, start here: Editors Alley Topic
Then contact Bill with a Private Message

Designed a USB device around an STM32F105

Talk about "WhatEVER !"..
Post Reply
Message
Author
Heapme
Posts: 1
Joined: Wed Dec 27, 2017 4:54 am
Location: Shenzhen, Guangdong, China

Designed a USB device around an STM32F105

#1 Post by Heapme » Thu Dec 28, 2017 3:49 am

I have designed a USB device around an STM32F105(datasheet: www.kynix.com/uploadfiles/pdf65976/STM32F105R8T6.pdf). It is USB 2.0 Full Speed CDC device configured as a Virtual COM Port using ST's USB Library. It uses the STM32's built-in PHY, and runs at 12 Mbps.

I'm sending data in 254-byte packets. Occasionally (averaging 1 in 17000 packets) the host computer receives bad data. It is generally constrained to a single byte in the packet.

So I'm looking at the signals using a Tektronix TDS2025 O-scope (200 Mhz).

Most of the transitions look great:
https://i.stack.imgur.com/RdlN9.jpg

But my low-tech eye diagram shows something unexpected:
https://i.stack.imgur.com/oUq7N.jpg

I managed to trap one of the bad waveforms, which looks like this:
https://i.stack.imgur.com/6N636.jpg

What might be causing this? I'm not sure where to start looking.

When I first plug in the device, the enumeration takes place successfully, and the eye diagram looks clean. But once I open the COM Port (using PuTTY, Hercules, or my custom java software), the glitches show up. I'm using a Lenovo Thinkpad with Windows 7.

Here is a picture of the layout:
https://i.stack.imgur.com/UNOju.jpg

The TVS IC is an NXP PRTR5V0U2F, and the Charger Detector is a TI BQ24392.

The USB traces travel about an inch on the back side of the board, then they come back up and connect directly to the microcontroller's USB pins. They are impedance controlled and appropriately length-matched to each other.

I'm probing from the USB connector's solder pads to the ground point which I've labeled on the picture. The probe had a short ground spring, not a long alligator clip.

If more data would help, please let me know. Also, this is my first USB device, and my first eye diagram test. If you see something wrong with my setup or assumptions, please let me know.

RealBlackStuff
Admin
Admin
Posts: 19163
Joined: Mon Sep 18, 2006 5:17 am
Location: Mt. Cobb, PA
Contact:

Re: Designed a USB device around an STM32F105

#2 Post by RealBlackStuff » Thu Dec 28, 2017 4:25 am

This is so far off-topic, it's not even funny!

Also please read the Forum Rules viewtopic.php?f=16&t=14339 before you post!

Post Reply
  • Similar Topics
    Replies
    Views
    Last post

Return to “Off-Topic Stuff”

Who is online

Users browsing this forum: No registered users and 8 guests