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Questions on pin connection

Anonymous
Anonymous

Hi All,

I would like to ask some questions on pin connection.

 

I used Excel’s conditional formatting to highlight pins according to their types and obtained a colored pin map (top view) like below:

                   

      

                 

 

All those cells in solid color are supply or ground pins:

1.      VSS = green

2.      DVDDR2 = orange

3.      DVDD33 = blue

4.      CVDD = red

 

And all those underlined are DDR2 related pins. Are those with bold font in deep green are pins that are multiplexed with GPIO.

 

My question is how should I deal with unused pins? I do not have an idea with pins that are

1.      Unused

2.      Not multiplexed GPIO

yet, but with unused GPIO pins, since its I/O direction can be toggled by program, I think it is bad to leave it as an input for which external signal could affect its logic gate, so mostly likely I should toggle it as OUTPUT, and leave it unconnected.

 

Is it correct? Or should I set it as output, and either

1.      Set value high, and connect to DVDD33

2.      Set value low, and connect to VSS

?

 

Which is recommended?

 

On the other hand, I have found that most of GPIO multiplexed pins have either IPD or IPU. If they already have pulling resistors, does this mean I can also safely

1.      Set them as INPUT

2.      And

                                i.            Connect to DVDD33 if it has IPU

                              ii.            Connect to VSS if it has IPD

 

Logically, all the above solutions (either as OUTPUT or INPUT and making their associated connections) seem would work. But practically, which is better? What is TI’s recommendation?

 

 

My last question is on IPU and IPD resistors. Since pins with such description are described as having the ability to internally turn on a puling resistor, then how large resistance (in Ohm) does these resistors offer? Since they are situated within the silicon ship, then it seems unlikely that they can be made using material of common external ZWT or through-hole resistors, so what are they made of? Someone told me that they are something like “MOS resistor”, is it true?

 

And for GPIO pins with IPD or IPU, do I still need to connect an external pulling resistor when they are used as input pins?

 

 

 

Thanks,

Zheng

  • Anonymous
    0 Anonymous in reply to Varada Bellary

    Dear Varada,

    I get the following error message:

    "Group Not Found. The requested Group cannot be found. "

    Does the page still exist?

     

    Zheng

  • 0 in reply to Anonymous
    TI__Expert 5750 points

    I am quoting from the original post. These are general guidelines titled : "What to do with unused pins in DM355/DM335"

    This questions keep coming up very often. So in the intent to have this information more widely available I am adding this announcement for this Forum.

    There are 2 categories of unused pins.

    1) Pins that do not have any function, meaning they are not connected to the die: normally we leave those unconnected.

    2) Pins that do have a function but are not being used, e.g. ASP xmit pins if they are not used. In that case, we normally tell customers three things:

    a) If the pin is an input AND has an internal pullup or pulldown AND is not routed on the board, leave it unconnected.

    b) If the pin is an input AND has an internal pullup or pulldown AND is routed on the board, put an external pullup or pulldown (try not to oppose the internal PU or PD to save power).

    c) If the pin is an output pin, you can leave it unconnected.  Sometimes output pins become high-z when not active, therefore, it is still a better idea to add external pullup or pulldown resistors, assuming there is enough board space for them.

    Regards,

    Miguel

  • Anonymous
    0 Anonymous in reply to Varada Bellary

    Dear Varada,

     

     

    For 2), Miguel classified three mutually exclusive cases. But what about for GPIO pins? In order to ensure it falls in one particular case, does the user need to first programmatically set whether it is INPUT or OUTPUT? And during booting time such that the code has not yet run, what is the default state of GPIO pins? Will there be a problem?

    And from http://processors.wiki.ti.com/index.php/Optimizing_IO_Power_Consumption,

     Is this a good advice?

     

     

    Another question is that I don't quite understand the current source and the leakage mechanism in Fig 3 there. Is the current source of the transistor type? Why does the leakage in the 3rd and 5th case?

     

     

    Zheng