User Manual

MHX-920 Operating Manual: Chapter 3 Modes of Operation 11
3. Modes of Operation
The MHX-920 modem can be easily configured to meet a wide range of
needs and applications. The module is designed such that all communication
is through one serial port (Pins 21 to 28 on the module). This port has two
functions:
1. It provides the asynchronous interface with the host equipment for data
that is sent/received on the RF channel. When operating in this fashion,
the module is said to be in data mode.
2. It is also used for configuring and programming the module. When
operating in this fashion, the module is said to be in command mode.
In addition to data mode and command mode, there is a third mode of
operation called diagnostics mode. The module will always be in one of
these three modes.
3.1 Data Mode
Data mode is the normal operating mode of the MHX-920. When in data
mode, the MHX-920 is communicating with other MHX-920 modules, and
facilitating wireless asynchronous serial communication amongst two or more
terminal devices. There are three basic elements to any MHX-920
communications network:
• One module configured as the Master
• Zero or more modules configured as Repeaters
• One or more modules configured as Slaves
The function of the Master is to provide synchronization for the entire
network, and to control the flow of data. There is always one Master per
network. The Master is the ultimate destination for all data collected at the
various Repeater’s and Slave’s serial ports. With the network set up for
Point-to-Multipoint communication, all data received at the Master’s serial
port is transmitted to every Repeater and Slave in the network. The MHX-
920 is a frequency hopping transceiver, meaning that it “hops” to a new
frequency after a predetermined time interval. This time interval is a fixed
time set by the user, and can range from 8ms to 120ms. The MHX-920 hops
according to a pseudorandom pattern of 50 different channels.
When configured as a Slave, the MHX-920 searches for synchronization with
a Master. Network topologies consisting of a single Master and virtually any
combination of Slaves and Repeaters may be deployed. The functionality of
any particular MHX-920 can be configured as follows: