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Message
From: Thomas Winkler<tc@t...>
Date: Fri Feb 8 11:30:09 CET 2008
Subject: [oc] I2C core questions (Avalon, SOPC)
Hello,> It's generally good practice to _NOT_ have any bidir ports in your design
> except for the topmost level. Technically, internal bidir ports can't be
> synthesized anyway, and synthesis tools just make it look like you can.
> The way this is done has changed in Quartus, for example, in the last few
> versions and has caused problems with some older designs that I have
> re-built recently.
Ok - that means that I should not have scl and sda as inout ports in my
i2c_master_top_avalon.vhd file? My idea was to add the tri-state logic to
this file and define the ports as "inout" since i do not intend to use SCL
and SDA internally anyway but bring them out to the board pins.
> [...] I wanted to use it to (also)
> interface to on-chip peripherals, and so had to change the interface.
Ok - that absolutely makes sense to me. But since I (for now) only intend to
interface off-chips peripherals my code should be ok, right?
> Maybe this is related to my comment above??? I'm assuming you have a
> top-level wrapper around the SOPC-generated VHD - yes? What type of port
> do you have specified for SCL/SDA there? If not, it's generally a good
> idea to do so...
Yes - but my toplevel wrapper is a schematic but not a VHDL file. But the
principle should be the same. In my previous version I hat a mistake
regarding the SCL and SDA ports in the schematic. Now the are bidi ports as
they should be. See: http://www.wnk.at/tmp/i2c/toplevel.png
> The cyclone parts have a weak internal pullup option which you need to
> specify in the assignments editor - IIRC around 22K? Depending on your
> external bus/peripheral that may or may not be sufficient.
Ok - I now found out how to set the pull-up in the pin assignment editor:
http://www.wnk.at/tmp/i2c/pin_assignment_2.png
I now measure ~3.1V on the idle SDA pin but get 0V on the SCL pin which
confuses me. I'm not sure whats wrong with this one.
Do you have any idea?
Thank you,
--
Thomas Winkler
tc@t...
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