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Dear Sir,
I met one problem as the attachment. The voltage drop is supposed caused by the pin to pin impedance, I guess. Because pin to pin resistance is about ony 30K to 40K Ohms which is much lower than that in MAXII micro. The emulation board that I'm using is the DE2-70. When I use the board to design an I2C to drive an external LCM through GPIO 0 and a ribbon bus. I've gotten a waveform as the attachment. After checking, I found the pin to pin resistance isn't as high as that in MAXII micro. I don't know how many ohms are appropriate in general? The pull-up resistors that I use are FPGA internal pull-up resistors. Suppose, the values of the internal pull-up are close to the pin to pin resistance. Are there anyone has idea about the issue? Thank you! Regards, Peter ChangLink Copied
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From your draqing: Problably the pull up on the SDA/SCL line is too high. For most I2C busses the internal pull ups of fpga's are to high in value. A 4.7kOhm pull up on the lines is a good starting point. Or some device is loading the bus ...
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Hi Johannes,
You're right. The high pull-up is one of the problem. But I'm using a FPGA internal pull-up. I'm not quite sure how large it is. I may only estimate it based on the voltage level I could see. I don't know if it is able to be set. Anyway, from the point of view, to solve the problem, I may only use an external pull-up. Do you think so? Thank you! Peter Chang
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