DP83849IF strap options

Amanda,

Which pin is missing the external pull and which functionality are you needing to strap (i.e. enabled or disabled)?  With the exception of the SNI_MODE strap, the pins used for straps are outputs during normal operation.  Adding a wire to another external pull would short the outputs together.  Even if one of the outputs were unused in your implementation (e.g. an LED you have not chosen to use), it would not be good to short them together.

The strap pins do have internal pulls.  If you are adding the external pull in the same direction as the internal pull, you won't need to make any changes.  The internal pull should be sufficient by itself.

We also have a software utility to access the device registers using a parallel port cable.  Using the utility might require some minor modifications (i.e. cut and jumper a trace or two) to the board during prototyping, but it could help you get a head start on testing the hardware while you wait for the software to be ready.  The utility is called ALP (Analog Launch Pad) or Integrity and is available for download at:

http://www.ti.com/tool/phytera-ethernetintegrity-sw

If you choose to use the utility, I can help you determine the best way to connect to the device and get you up and running.

Patrick

Hi Patrick,

I'd forgotten that the function of the strap pins change after power up so it isn't a good idea to tie them together.

I'm trying to enable pin 56, extender_en, to get single clock MII.  I've got a development board and have used the ethernet integrity software.  Unfortunately I've just gone back to double check the setup and noticed that I'd missed this pull-up.  I think that I must have just assumed that because my device will be functioning as a media converter I didn't need to enable extender mode; without reading the full description of this option.  I really should have done this before sending the design out.

I'll add another resistor onto my board and link it to pin 56 and my 3.3V supply.  A blob of epoxy should help it pass qualification testing.

Thanks for your help,

Amanda

Hi,

I've updated my design to add a pull-up resistor and wire links.  I've now been asked what will happen if the configuration resistors were to fail short circuit.  This would pull all of the pins with strap resistors to 3.3V or 0V.  I'm not using the dual function of the pins but could this cause problems internally?

I've attached a copy of my circuit.

4431.DP83849IF.pdf

Thanks, Amanda

Amanda,

I want to make sure I understand the question.  Are you wanting to know what will happen if the various strap resistors short such that the corresponding pin will connect directly to the supply? 

Also, I assume that this is a straightforward MII implementation with the TX and RX MII signals connected to a MAC.  Presumably these connections exist in the actual schematic, but are not shown here.  Is that correct? 

Patrick

Hi Patrick,

Sorry I should have explained myself a bit better.

Yes, I'd like to know what will happen if the pins were to get connected directly to the supply.

I forgot that the schematic doesn't show my missing pull-up resistor on pin 56 (extender_en).

My board is setup in media converter mode with port A connecting to the electrical port and port B connecting to the optical device.  The MDC and MDIO pins are connected to a microcontroller which will allow interrogation of the registers (once the software is written).

There isn't a connection to a MAC.

Thanks, Amanda