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AR# 24049

EDK OPB IIC - Data read from the IIC EEPROM does not match the data written to the IIC EEPROM on the ML403 Evaluation Board

Description

The ML403 is not meeting the rise time on IIC_SCL and IIC_SDA signals according to the IIC bus specification. I verified that the IIC failures do not exist when the strong (1.2K) resistors are used for R70 and R71 resistors.

Solution

Measure the rise time of the IIC_SCL and IIC_SDA signals. Depending upon the mode of operation supported, stronger pull-up resistors might need to be installed. Caution must be taken for the mode of operation supported. The IIC rise time for standard mode of operation is 1000 ns (max); however, the IIC rise time for fast mode of operation is 300 ns (max). Select a resistor value to meet the rise time requirement for the mode of operation that must be supported. Also, the IIC IO signals can sink a maximum of 6 mA, so you must take care to choose a resistor value that does not exceed this.

For example, if 10K ohm resistors are used to pull-up the IIC_SDA and IIC_SCL signals, and the voltage source to the resistors is 2.5V, this would equate to a current of 2.5V/10000 ohms = 0.25mA.

Refer to the I2C-bus specification in the "Philips IIC bus, v2.1, release January 2000" for application information.

AR# 24049
Date Created 09/04/2007
Last Updated 12/15/2012
Status Active
Type General Article