Chapter 2: Hardware Information
NEO
Expansion Port Theory of Operation
Psion Teklogix
NEO
HDK User Manual
17
This current should be considered as peak and current use at this level should be restricted to
100 ms duration with a repetition rate greater than 5 seconds. The average current drawn
through this interface should be 500 mA or less.
Reliable connections are necessary to provide power to the expansion module. It is expected
that the connector surface will be cleaned before installation and sealed when in use. This
will ensure that the multiple VCC and ground contacts effectively share the current.
When the USB-based device is attached to the expansion port it will be detected by a polling
process running on the PCon. To detect the presence of expansion hardware, the PCon first
asserts the pull-up resistor (P1.4), then reads the state of the EXP_DETECT signal (P1.3). A
low state indicates that hardware is attached. When no devices are present, PCon will not
turn on power to the expansion port. When a device is present, PCon will allow power to be
turned on to the expansion port and will continue to monitor for device presence.
Once powered, the expansion device establishes a connection over USB and communicates
its type, revision, etc. over USB.
Should a connected expansion device be detected as not present, power will be removed
from the interface. For safety reasons, software prevents re-application of power until the
device is detected once more.
When the
NEO
is docked, power to the expansion port is removed. Power can optionally be
re-applied once the hand-held is removed from the dock, unless the expansion device has
been detected as not present.
Note: When using the PX3004 Quad charging station, the available current per charger
slot is insufficient to allow the
NEO
to be turned on, to power the expansion slot,
and to charge the battery, all at the same time.
