Is a pullup or pulldown required for A20 to A24 on a rabbit4000?

I’m using a 4mB flash and 2 each 2mB static rams. In reviewing some of the rabbit schematics that use A20, I don’t see any pull up or pull down resistors. On reset these lines are not in a known state, so I’m wondering are resistors needed and if not why?


If you are designing your own core module from the Rabbit 4000 I recommend that you follow the design guidelines set out in the Designers Handbook linked here

From section 3.2:

Floating inputs or inputs that are not solidly either high or low can draw current because both N and P
FETs can turn on at the same time. To avoid excessive power consumption, floating inputs should not be
included in a design (except that some inputs may float briefly during power-on sequencing). Most unused
inputs on the Rabbit 4000 can be made into outputs by proper software initialization to remove the floating
property. Pull-up resistors will be needed on a few inputs that cannot be programmed as outputs. An alternative
to a pull-up resistor is to tie an unused output to the unused inputs. If pull-up (or pull-down) resistors
are required, they should be made as large as possible if the circuit in question has a substantial part of
its duty cycle with current flowing through the resistor.

Hello, The below document might be helpful while designing with rabbit core modules