MPCS: A Wireless Communication Protocol for Ubiquitous Industrial Environment - Advanced Research on Computer Education, Simulation and Modeling - page 408

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Fig. 2. A ZigBee Gateway

flash memory, 8-KB RAM, and other powerful peripherals. Fig 2 is a ZigBee gate-
way. The gateway consists of CC2530, SP3220E devices, battery and some interfaces.
Because PLC has a UART interface and the interface usually is RS-232. But
UART of CC2530 is TTL, so RS232-TTL conversion is done with a SP3220E chip.
ZigBee gateway allows device containing UART to communicate via radio with
other devices. Each device connects to ZigBee gateway. In this system, the four Zig-
Bee gateways provide the radio communication link.
When the ZigBee gateway is used in an application, it is assumed that a permanent
power source will be available at both ends of the wireless link. This means the on-
chip radio can always be active, eliminating the need to synchronize the transmis-
sion/reception of data. The link is designed to operate at up to 19200 baud.
The ZigBee gateway of PC must act as a PAN Coordinator. The PAN Coordinator
is responsible for starting the network and allocating an address to the other gateway,
which acts as a Router. Fig 3 is the program flow chart of PAN Coordinator.
The ZigBee gateway of PLC acts as a router device. The router device scans the
radio channels, looking for the PAN Coordinator. Once it has found the Coordinator,
it associates with it. Data transfer between radio and the on-chip UART is identical to
that described above. Data received via the radio is output to the connected device
using the on-chip UART, and data received by the on-chip UART from the device is
transmitted over the radio. This process is repeated every 20ms. Fig 4 is the program
flow chart of Router.

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Fig. 3. Coordinator Program