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Altera_Forum
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12 years ago

Getting data from a rtc device through I2C

Hi all, I would like to retrieve information from a RTC device which is directly connected to a GPIO, using the i2c protocol. So, the first step was to load the i2c-gpio driver with this piece ...
Altera_Forum's avatar
Altera_Forum
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12 years ago

Hi,

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On the 9th SCL's rising edge I get a half voltage level which is interpreted as a NAK by the i2cdetect utility. This curious case disappears if I configure the SCL as "output only". This brings me to think about my pins configuration: as the SCL and SDA lines are open drained, I configured them as such.

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Did you make the SCL and SDA 'hardware pins' open-drain ? It seems that a bus fighting occurs. The SDA line is used bidirectionally, your FPGA pin must be tri-state when the slave returns the ACK (= 0) signal. The open-drain pin is a simple method to achieve this. The SCL pin can be 'output only' if you don't have other I2C master except your FPGA.

Kazu