You may also want to refer to the Due Reference design http://arduino.cc/en/uploads/Main/arduino-Due-schematic.pdf. Note that in the reference design SCL0 and SDA0 each have a 1k pull-up to 3v (see I2C voltage translator on the lower right side) while SCL1 (pin 70) and SDA1(pin 9) do not appear to have a pull-up. This seems to agree with the UDOO Also, this post on the arduino Forums confirms that you do need to add pull-up resistors for SCL1 and SDA1 http://forum.arduino.cc/index.php?PHPSESSID=ub3kncqamgqcttapvrgmu4kv65&topic=223513.0
The due and the udoo due may be different, if the schematics are true the udoo is fitted 4.7k resistors instead of 1k. I've used both I2C ports on the udoo and they work without any resistor fitted, Any pin as 3 ways to refer to it , the board numbering on the edge connecters , the pin numbering on the chips , or the port number of the chip , so pin1 , pin2 , pa0_3 could be a way to refer to the same pin.
I asked the question on the Arduino board and now for a second time I was told that you do need to add pull-up resistors for SCL1 and SDA1. (see Palliser's http://forum.arduino.cc/index.php?PHPSESSID=gtqffk43o13kigglshjgvq7ft3&topic=229799.0) I was also refereed to this post http://forum.arduino.cc/index.php?PHPSESSID=kmvv9bq71td9nn6b882ol5kjh2&topic=132130.0 Which explains the differences between physical pin numbers (70 & 9) versus digital pin numbers (71 & 70) used in the Due reference design. I don't doubt that the Due I2C1 (SCL1 & SDA1) may work for some without pull-up resistors, but its not working on my UDOO Quad and others seem to be having these problems as well.
That`s like going on a volkswagen forum and asking if the oil is easy to change , AND not saying that you have a Ford car. The Arduino Due may not contain pull up resistors , BUT you are on the udoo forum which may contain the Due chip and may be compatible , BUT may have added or change components. Sorry , what are you asking ? , does the Arduino Due have pull up resistor or the udoo ? All I can say for sure is that I`ve tried using a mcp23008 / mcp23017 circuit , which worked on both port on the Arduino side without pull up resistors fitted , and that circuit would not work without some sort of high bias. I would try going back to basics !!! Does the THING still work on a atmel Arduino ? Does the pins work ? , eg set to output and toggle them with a led , so you know you pin aren`t blown. Have you got the correct I2c Address ?
Peter247: Please be civil. The UDOO claims to have a Due, The UDOO schematic set does not show pull-up resistors for SCL1 or SDA1, the Arduino reference design does not have pull-up resistors for for SCL1 or SDA1, You claim pull-ups are not required. My UDOO's SCL0 and SDA0 works, but SCL1 and SDA1 do not. I'm using a scope on these pins and the I2C scanner. I don't have pull-up resistors at home at the moment to test, but will once I get them. There's conflicting information on this board, and AdaFruit forums that makes the shields. That's why I went to the Arduino site since they control the Due reference design. I understand that there may be differences between the UDOO implementation of the Due and a real Due, but have seen nothing to indicate that the I2C is different. If there are pull-ups for SCL1 and SDA1, then where are they in the schematics for the UDOO? The ones shown on page 6 are for SCL0 and SDA0. If I'm in error, then my UDOO is not functioning correctly and I stand corrected and apologize, but this has nothing to do with changing oil in any make of vehicle
Sorry I am being civil !!! First we are going back to what already been established. The schematic set DOES show pull-up resistors !!! No , I say they are already fitted on_board . I2C scanner sketch does not work , they is a fault in the library / parts do not full function , but the main parts of it does. What I`m trying to say , is that the Arduino Due and the Arduino Due inside the udoo may be different OR should I say are different. So what's true about the Arduino Due may not be true about the udoo and its Arduino Due . Compatible is not the same.
Peter247 Those resistors pull-up SCL0 and SDA0 on pins J5 pins 1&2, but the Motor shield uses the other I2C (SCL1 and SDA1) on J21 pins 9&10. Its the second I2C which doesn't seem to have pull-ups.
Obviously this is one I will never win, because no matter what evidence I will give you it will just be ignored, so this is my last post on this topic. Good bye and I hope you get your motor shield working in the end.
