Chapter 2: Hardware Information
NEO
Expansion Port Theory of Operation
16
Psion Teklogix
NEO
HDK User Manual
The TRIGGER input signal is used to activate the built-in data capture scanner.
The DETECT input signal is sampled to detect an attached expansion device. An expansion
module must pull the DETECT input low to indicate that it is attached. When an expansion
device is detected, the
PCon
(peripheral controller) will allow the output power to be en-
abled. If the DETECT input goes high at any time, the PCon shuts off the output power,
which cannot be reapplied until the attached device is detected again.
The
NEO
expansion port is designed with two basic classes of expansion in mind:
Trigger
operation
and
USB operation
.
Trigger Operation
Trigger operation expansion devices provide a simple trigger to the
NEO
. These devices
have no active electronics and involve a trigger switch.
When the user actuates the trigger, a PCon signal (EXP_~TRIG) is pulled to DGND. By de-
fault, and if a scanner is installed, the
NEO
begins scanning for a bar code. Software in the
NEO
provides the necessary de-bounce conditioning of the trigger signal on this input. The
default trigger mapping can be configured through the Manage Triggers applet in the
NEO
Control Panel. Alternatively, the trigger mapping can be removed and the developer can use
it for his own purposes through the Trigger namespace in the Psion Teklogix Mobile
Devices SDK, available for download on the Psion Teklogix community website
(
http://community.psionteklogix.com
).
USB Operation
USB operation expansion devices contain electronics and are intended for RFID readers and
other active devices.
Communication between the host unit and add-on devices is done using USB signaling.
Since the power requirement for the add-on devices is not yet determined, the expansion de-
vice’s power supply is designed to derive from the VCC_BATT, rather than 5V for USB.
This provides the most flexibility. The power can be turned on/off by the
NEO
PCon, as
long as the attached device is detected.
The voltage range is between 2.7 V and 5 V; the add-on device should condition its input
power to handle the input voltage range while still maintaining proper output
voltage/current.
The switched power at the expansion connector is specified at a nominal 1000 mA. The
current limit is set by a resistor on the
NEO
main logic board.
