P4040 Reset Configuration Specific FAQs

Document created by Omar Cruz Lopez Employee on Aug 6, 2012
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Do we have an internal pull up on LA20 pin in P4040E?

According to hardware spec for P4040, LA20 pin is a reset configuration pin. It has a weak internal pull-up P-FET which is enabled only when the processor is in the reset state. This pull-up is designed such that it can be overpowered by an external 4.7-kΩ pull-down resistor.

Assuming that I did not include a pull up or pull down and assuming no device was asserting LA20--what state do we sample at POR? If LA20 is left floating at POR, would one read the SVR for P4040E (80ED0211) OR P1011E (80ED0011)?

According to hardware spec for P4040, LA20 pin "must be pulled down with a 4.7K resistor". So the default in case that a design doesn't include an external pull (as required by the spec) is for it to sample as a '1'. Leaving the pin NC (floating) at POR is effectively an out of spec configuration.