In 21489 EZ board schematics, there are series termination resistors of 33 ohms present at DAI/DPI pins.
What is the purpose of this and is it absolutely necessary to have it.
Thanks and Regards
The series termination resistors are used to reduce the unwanted EMI. The output impedance plus a series resistor near the output should match the impedance of the signal trace on the printed circuit board.
Kindly refer page 915/1276 of the ADSP-214xx “Hardware Reference Manual rev1.0” which says that these series termination resistors are used to prevent glitches on signal transition and maintain signal integrity.
The link for the manual is given below:
Please let me know in case you have any further doubts/queries.
Thank you for the reply.
I have already checked in both the manual and EZ board schematics.
It says the series termination resistors are required only on edge sensitive inputs or outputs.
In my design all the DAI pins are connected to SPORT emulated in FPGA and DPI pins for SPI and Flags.
These series termination resistors are not present in the first revision of my board and everything is working fine.
Now because of some changes we need a second revision and i wanted to know is it absolutely necessary to have the series termination resistors.
I had a similar discussion with our EZ-Kit design team sometime back regarding this. According to them,
"The series termination resistors on the 214xx EZ-KIT were added because we have EZ-Extenders (ie Sharc Audio EZ-Extender) that would need to interface and work with the respective EZ-KITs.
In general if the room and cost allow for it, it is better to have series terminators since once the boards are back we have more flexibility to look at the signal integrity of the signal and change the values based on scope measurement.
Also as a general rule, if the net is longer than 5-6” and there are multiple loads, series terminators might be needed to help reduce any reflections that may occur due to mismatch in line impedance."
Having said that, I don't think there is any other specific recommendation other than what's is mentioned in the HRM as far as SHARC is concerned. You may follow general board design guidelines to decide whether or not you need a series termination on these signals and if needed what exact values should be used.
Hope this helps.
Retrieving data ...