 SERIAL DATA LINKS
Wireless serial links ..... RS232 or RS485
The ELPRO 405U radio modem module provides RS232 or RS485 connections by radio. It can be used instead of serial cable to link PLC's, data loggers, supervisory computers and intelligent transducers. The 405U has been designed to be easy to use and simple to install. It uses a low power UHF radio which does not require a radio licence*. The module is fully integrated with radio, power supply, serial ports and microprocessor controller housed in a strong industrial aluminium case.
*dependent on the radio regulations in each country
Simple and Reliable
The 405U includes a radio transceiver, allowing communications in both directions, so the modules can check and control the transfer of information. The 405U is suitable for both simple and complex systems. It can operate in a transparent mode, where the host devices provide error checking and communications control. For less intelligent host devices, the 405U can provide the addressing, error checking and control of communications. The 405U can also accept Hayes compatible commands for selective addressing.
High Speed Wireless Data
Host devices can connect to the 405U via RS232 or RS485 serial ports, at data rates up to 38.4Kb. The 405U has an internal buffer of 4Kbytes, and the radio can transmit data packages configurable between 45 and 300 bytes, at speeds configurable up to 9600 bits/sec. The 405U radio modem is both low cost and very flexible.
Radio Communications
The 405U operates in the 400 - 500 MHz UHF band. Most countries provide low power licence-free channels for use without the need for an individual radio licence. The 405U radio is available with transmit powers between l0mW and 500mW, which meets the low power regulations of most countries. The 405U has been designed to operate reliably on an open licence-free channel with other users. The expected radio range of the 405U is l.5km(l0mW) to 10km(500mW) "line of sight" at 4800 bits/sec. The 405U module may also be configured to act as an intermediate repeater to provide longer radio paths. Up to five repeater modules may be configured for each link. The transmission rate of the 405U radio may be configured between 1200 and 9600 bits/sec, half-duplex.
RS232/485
The 405U connects to host devices using RS232 full duplex or R5485 half duplex. The RS232 connection provides standard CTS/RTS control, with the 405U module operating as a DCE device. The CTS/RTS signals may be configured to reflect the status of the 405U input buffer, or to reflect the CT5/RTS signals at the remote module. The R5485 connection is a industry standard half-duplex twisted pair mulitdrop connection. Only one serial connection (R5232 or RS485) can be supported at each module, however different types of serial data can be connected to different modules in the same system.
The 405U accepts data at standard rates between 75 and 38400 baud. It may be configured to accept 10-bit or 11-bit characters, with 7 or 8 data bits, even/odd/no parity, and 1 or 2 start and stop bits. The 405U will connect to almost any host device!
Configuration
The 405U module may be configured to operate in two different modes, to suit the type of host device. In each mode, data is sent in packets of up to 300 bytes, with a superimposed "system address". Only a module with the same system address will accept data from another module - this avoids cross-talk between systems operating in the same radio range. Modules may be configured using on-board miniature switches. Some parameters may be configured by the host device using standard Hayes codes.
Transparent Mode
Transparent mode is suitable for host devices which provide their own data checking and control the flow of data. As data is received at the serial port, it is transmitted by radio and re-created at the serial port of all other modules with the same system address. There is no error checking carried out by the 405U modules and modules are not individually addressed - this is performed by the host devices.
Modules listen to the radio channel and hold off transmitting until the channel is clear, apart from this there is no other transmission delay. Transparent mode is suitable for PLC networks, or for a broadcast system where the same serial data is to be sent to multiple devices. In transparent mode, one repeater may be configured - the repeater will re-transmit any radio message it receives.
Controlled Mode
In controlled mode, each module is configured with a unit address, and the 405U modules perform error checking and acknowledgments. If a message is corrupted during the radio transmission, the source module will re-transmit the data up to four times until the data is received correctly. If reliable radio communications cannot be achieved, a communications failure output is provided as a discrete signal.
Controlled mode is suitable for host devices such as data loggers or intelligent transducers which do not carry out error checking or control the flow of data. In controlled mode, up to five intermediate repeaters may be configured in any one link. Destination addresses, and repeater messages may be preset using the configuration switches on the module, or they may be set from the host device using standard Hayes AT codes. This type of system would be suitable for a master device (such as a PC) polling several slave devices (for example, data loggers) to download information.
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