F2812: can XINTF be disabled?

allegrocantabile said:

The following questionnaire are related XINTF functions.   My setup does not use XINTF and was wondering if there were any way to turn off the module.  We have a few concerns with noise and some input pin termination. 

 

Q4.  Is there any possible way to turn off XINTF?  I did not see any notes on settings regarding disabling XINTF in spru174 or spru067c.  Any documents I should look at? 

Q5.  Would holding ~XHOLDA pin be a viable way to disable the XINTF module?

Q6.  If no external memory device was used, should input only pin be pulled-up/down? 

Hi,

We had some discussions internally on this - I'm posting the responses to close the loop:

Tim Love said:

In general there is not just a bit you can set to disable the XINTF. If this bus is not being used, a simple way to handle most of signals is to pull the XHOLD in low. Please see the description of XHOLD on page 35 of the XINTF Reference Guide:

 

This signal, when active low, requests the XINTF to release the external bus (place all busses and strobes into high-impedance state). The XINTF releases the bus

when any current access is complete and there are no pending accesses on the XINTF. This signal is an asynchronous input and is synchronized by XTIMCLK.

 

This will place the Address and Data busses as well as the strobes into high impedance. Now the only pins left are the XCLKOUT, XREADY, XHOLDA, and XMP/MC. (The list of signals is on pages 34 and 35). XCLKOUT can be disabled through setting the CLKOFF bit in the XINTCNF2 register. XHOLDA will be driven low when the XHOLD request is granted. XMP/MC is used for enabling the internal Boot ROM or Zone 7. This should be pulled low for standalone operation. XREADY is an input and can be terminated.

 

With that being said, make sure that code is only run from internal memory. If an access is attempted to the external interface the CPU will be stalled until XHOLD signal is removed.

Regards,

 

Tim Love 

Tim Love said:

Some additional thought on this issue. The XHOLD solution will work as described. The inputs have an internal pullup so they shouldn't float. But really it is not necessary to place the pins in HI-Z. The same outcome can be acheived by:

1) Leaving the outputs (Address and output only control pins) unconnected as they will not oscillate and introduce noise into the system

2)  The input pins (HOLD and READY) can be tied to VDDIO

3) The XD bus could actually be tied to either GND or VDDIO. They have internal pull-ups but you could add external resistors for added reliability

For further information, there is a section in the Hardware Design Guidelines app note that discusses terminating unused IOs.

http://focus.ti.com/lit/an/spraas1a/spraas1a.pdf

Regards,

Tim Love