Layout Notes; Recommended Pull-Down Resistors; Alternate Function During Standby And Sleep Mode; Reduce Power During Standby And Sleep Mode - Intel PXA27 Series Design Manual

Keypad Interface
18.4

Layout Notes

This section has information on the best method for connecting to the keypad interface with a pull-
down resistor and appropriate implementation during standby and sleep mode.
18.4.1

Recommended Pull-down Resistors

The recommended pull-down resistor value to minimize power usage is 100 K Ω . The
recommendation is not to have a pull-up resistor because the value needed to overpower the
internal pull-down resistance during stand-by and sleep mode would consume excessive power
during normal operation mode.
18.4.2

Alternate Function During Standby and Sleep Mode

During the transition into standby or sleep mode, the matrix keypad and direct key signals change
to their respective GPIO function. The operation of these pins are determined by their
corresponding GPIO settings.
18.4.3

Reduce Power During Standby and Sleep Mode

Using the appropriate GPIO Pin-Direction Register (GPDR), the KP_DKIN and KP_MKIN
signals, interfacing to the keypad controller, must be configured as input signals to eliminate
excessive power usage caused by driving pull-down resistors. The KP_MKOUT signals used to
interface to a matrix keypad must be configured as output signals to eliminate excessive power
usage caused by having floating inputs on the KP_MKOUT signals.
18.4.4 Using the Keypad Signals to Wake-up from Standby and
Sleep Mode
It is possible to use the keypad signals to wake up the PXA27x processor from standby or sleep
modes by configuring the Power Manager Keyboard Wake-Up Enable Register (PKWR). After
wake-up, the Power Manager Keyboard Edge-Detect Status Register (PKSR) must be read to
determine which GPIO corresponding to the keypad input signal detected an edge transition.
18.4.5

How to Enable Specific Combinations of Direct Keys

The enabling bit field KPC[DKN] implies that all KP_DKINx signals must be enabled sequentially
from KP_DKIN0 to KP_DKIN7. This is true for this specific controller, but it is still possible not to
map any of the direct keypad signals to a specific ball on the PXA27x processor package by using
the PXA27x processor GPIO Alternate Function Registers (GAFR0/1/2/3). By not mapping a
specific direct input signal to the PXA27x processor package, a value of zero is read in and the
input is not left floating. Leaving the input floating causes excessive use of power.
II:18-4
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Intel PXA27x Processor Family Design Guide