RTcom Radio Modems - Manual (Page 17)

17
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 Max and Global a fee channel should be selected as far
away as possible from 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.
If a scanner is not available than once the link has been established plug in attenuators may be used
to determine the fade margin.
Finally, once the installation is complete it should be tested for conformance the EMC, Health and
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
TM
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
TM
TERMINAL.EXE and HYPER TERMINAL.EXE
Windows
TM
depending upon its version contains terminal (Terminal.EXE or Hyper Terminal.EXE)
programs that can be used to transfer files between two platforms. From experience we have found
the Windows
TM
3.11 version of Terminal.exe to be more reliable than the Windows
TM
95 version. The
98 version has however been improved but performance will vary from machine to machine. The
problem we believe with these programmes is the low priority placed on communications by the