Embedded Systems Conference
Breaking News
Newest First | Oldest First | Threaded View
User Rank
re: Understanding clock domain crossing issues
JoelB01   6/21/2013 7:00:03 PM
There is another issue with data coherency that you did not address. The trace delay for all bits in the "A" bus must be approximately the same, and should be less than the period of C2. Unfortunately, it is common to "false_path" the data from FA to FB, which allows the tools to violate this requirement. This is especially a problem in the case where C1 and C2 are asynchronous clocks that are nearly the same frequency, and that frequency is fairly high. For example, with a frequency of 400MHz, the C2 period is just 2.5ns. If A is a 6-bit Gray coded value, and the the data delay for most bits of A ~0.5ns, while the delay for A[1] is much larger (5.5ns, 2 full C2 clock cycles later), you can run into an issue where the receiver gets a Gray code sequence that can lead to problems: Sent: 001100 001101 001111 (bit 1 transitions) 001110 (bit 0 transitions) 001010 (bit 2 transitions) Received: 001100 001101 001100 (bit 0 transition!) 001010 (bit 1 and 2 transition) In this event, the Gray code that the receiver sees appears to have decremented (from 001101 to 001100), where it should have only incremented. We have been able to address this problem in the Xilinx FPGA tool flow using a TIMESPEC with DATAPATHONLY, but have not been able to find a solution for this issue in the Altera FPGA tool flow.

old account Frank Eory
User Rank
re: Understanding clock domain crossing issues
old account Frank Eory   5/31/2013 8:26:06 PM
Thanks for this excellent article and very thorough coverage of CDC problems and their solutions.

User Rank
re: Understanding clock domain crossing issues
I_B_GREEN   9/28/2012 5:29:50 PM
Your pictures gloss over hold up times

Top Comments of the Week
Like Us on Facebook

Datasheets.com Parts Search

185 million searchable parts
(please enter a part number or hit search to begin)
EE Life
Frankenstein's Fix, Teardowns, Sideshows, Design Contests, Reader Content & More
Max Maxfield

Awesome 3D Electronic Sculptures
Max Maxfield
I recently received an email from someone we'll call Martin (because that's his name). Martin's message was short and sweet. In its entirety it read: "You need to see this!"

Jack Ganssle, Embedded.com

Processor Pinups
Jack Ganssle, Embedded.com
My wife and I joke about our “adult” magazines. For her, those are the publications about beading. For me, they’re tool catalogs and Fine Woodworking magazine. The latter ...

Rajaram Regupathy, Cypress Semiconductor

Add USB Battery Charging Protocols to an Android-Based Design
Rajaram Regupathy, Cypress Semiconductor
Post a comment
Editorial Note: Excerpted from Unboxing Android: A hands on approach with real world examples, by Rajaram Regupathy, the author takes you through the process incorporating effective power ...

Rich Quinnell

Making the Grade in Industrial Design
Rich Quinnell
As every developer knows, there are the paper specifications for a product design, and then there are the real requirements. The paper specs are dry, bland, and rigidly numeric, making ...

Special Video Section
The LT8640 is a 42V, 5A synchronous step-down regulator ...
The LTC2000 high-speed DAC has low noise and excellent ...
How do you protect the load and ensure output continues to ...
General-purpose DACs have applications in instrumentation, ...
Linear Technology demonstrates its latest measurement ...
Demos from Maxim Integrated at Electronica 2014 show ...
Bosch CEO Stefan Finkbeiner shows off latest combo and ...
STMicroelectronics demoed this simple gesture control ...
Keysight shows you what signals lurk in real-time at 510MHz ...
TE Connectivity's clear-plastic, full-size model car shows ...
Why culture makes Linear Tech a winner.
Recently formed Architects of Modern Power consortium ...
Specially modified Corvette C7 Stingray responds to ex Indy ...
Avago’s ACPL-K30T is the first solid-state driver qualified ...
NXP launches its line of multi-gate, multifunction, ...
Doug Bailey, VP of marketing at Power Integrations, gives a ...
See how to ease software bring-up with DesignWare IP ...
DesignWare IP Prototyping Kits enable fast software ...
This video explores the LT3086, a new member of our LDO+ ...
In today’s modern electronic systems, the need for power ...
EE Times Senior Technical Editor Martin Rowe will interview EMC engineer Kenneth Wyatt.
Flash Poll