User manual

COMMISSIONING
The data rate, parity and number of data bits are set using the dual in line switch located above. If a
scanner is available the chosen channels and the adjacent channels should be scanned for activity.
With frequency agile products such as the -Global, a free channel should be selected as far away
as possible form the channel/s in use.
The antenna should be positioned and one modem connected and set to test mode. The scanner should
be used to measure the received signal strength. If the strength is >1uV, the link will normally work
however, a “fade margin” of > +10dB is preferable.
Finally, once the installation is complete, it should be tested for EMC conformance, Health & Safety and
Wiring Regulations etc. Exposed joints should be sealed using self-amalgamating tape and screw threads
coated with rust proofing compound.
COMMUNICATION PROTOCOLS
RTcom Protocol :
The RTcom™ Communication protocol does not make any attempt to correct communication errors. From
experience, the latency (delay) caused by error correction techniques is prohibitive for the majority of
applications. Further the use of a “transmit” buffer imposes a finite file size on the system and hence,
introduces the need for flow control lines such as DTR. Further, errors can occur in cabling due to induced
switching surges, nullifying any error protection on the radio link.
Proprietary Protocols :
The majority of our customers use a cable protocol that already employs error checking. This normally
comes in the form of a check sum appended to the end of the message. Similarly, addressing can be
appended to the message giving the destination of the data. Protocols such as MODBUS and EIBA Bus
handle these functions automatically.
Windows™ TERMINAL and HYPER TERMINAL :
Windows™ depending upon its version contains terminal (Terminal.EXE or HyperTerminal.EXE )
programs that can be used to transfer files between two platforms. From experience we have found that
Windows™ 3.11 version Terminal.exe to be far more reliable than the Windows™ 95 or 98 versions. The
98 version has however, been improved but performance will vary from machine to machine. The problem
we believe with these programs is the low priority placed on communications by the system. This results in
the messages becoming fragmented, thus confusing the modem into thinking the end of file has been
detected.
The other common problem, in particular with Windows™ Hyper Terminal, is the way in which it deals with
errors. Should an error occur it attempts to re-establish the link from both ends simultaneously, something
of course that can not be supported on a half duplex link.
Windows is a registered Trade Mark of the Microsoft Corporation