User Manual

SECTION 1: THEORY OF OPERATION
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Carrier Detect
The base station uses RSSI (received signal strength indicator) and software to generate a carrier detect
signal. Every millisecond, the microcontroller samples RSSI through an analog-to-digital converter. If the
microcontroller detects a step increase in the RSSI voltage (greater or equal to the RSSI step threshold
setting), a carrier detect signal is generated. This carrier detect signal is used to instruct the 4-level FSK
modems to search for an incoming data message.
Host Interface
The host interface is an RS232 serial port. The base station is a DTE (data terminal equipment) device.
Typically, only TXD, RXD and GROUND are used to connect to the host. The control signals are
available if required for a particular application. The recommended serial port settings are 19200 baud,
no parity, eight (8) data bits, and one (1) stop bit. These settings are user programmable.
The type of framing used on the host interface is configurable. It supports either RIM framing or SLIP
framing. RIM framing is the format used by previous generation IPMobileNet base stations.
The base station can also be used with an external modulation source. This is used when upgrading
existing IPMobileNet systems.
In addition to the host serial port, there is an INVADR Base Station I/O Board that is used for configuring
and monitoring the base station. A computer running a terminal emulation program can be connected to
this port. Its settings are 9600 baud, no parity, eight (8) data bits, and one (1) stop bit. The I/O board
also has additional connections used for testing purposes.
Time-Out-Timer
The microcontroller provides a programmable transmit time-out-timer function to eliminate the possibility
of inadvertent continuous transmit operation.
Front Panel Indicators
The microcontroller is responsible for controlling the illumination of the front panel indicators.
Receiver Injection
Functional block diagram of the receiver injection.