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AR# 60098

Zynq-7000 - PS I2C - Why does the PS I2C not meet the I2C spec?

Description

From I2C specification (http://www.nxp.com/documents/user_manual/UM10204.pdf), the requirement of rf is from 20ns*(VDD/5.5) to 300ns. (rf is the fall time of both SDA and SCL signals)

For the ZC702 Evaluation Platform, VDD is 1.8v so the requirement should be 6.54ns ~ 300ns.

I have tested this parameter of PS I2C on ZC702.

The tf @300KHz/400KHz on ZC702 is about 1.68ns. This does not meet the requirements of the I2C specification. 

Why is this the case?

Solution

The fall time (tF) of slow speed interfaces like I2C cannot be achieved by the I/O pads alone.
 
A proper external load capacitance on the pad is required to achieve the fall time.

As per the I2C specification, it should be 10 pF.
AR# 60098
Date Created 04/03/2014
Last Updated 04/28/2014
Status Active
Type General Article
Devices
  • SoC
Boards & Kits
  • Zynq-7000 All Programmable SoC Boards and Kits