Westermo RM-455U-D - Manual (Page 18)

Chapter One Introduction
Man_455U-D Rev 3.04 Page 19
1.8 Duty Cycle Limiting
Some licenses require that the modem limits its communications so that it is transmitting for
no more than a maximum proportion of the available time. This applies to European 500mW
unlicensed bands, where the modem must limit its duty cycle to 10%.
Duty cycle limit is set to 100% except for modems which are configured for the European
limited duty cycle bands.
To change the duty cycle limit, use the AT#D command. (AT#D100 for 100%).
Duty cycle limiting must be calculated over a time no greater than one hour. You might prefer
to calculate the duty cycle limit over a shorter time. The AT#T command sets the time in
minutes to use to calculate the duty cycle.
1.9 What Operating Mode to Use ?
1.9.1 Unacknowledged or Acknowledged mode?
Unacknowledged mode provides simpler operation as the units do not acknowledge
transmissions received. However confirmed operation in unacknowledged mode will only occur
if the host devices check the messages and return acknowledgments. Generally, if a device is able
to operate on a RS485 multi-drop serial link, it is suitable for unacknowledged mode.
The RS-485 port only operates in Unacknowledged mode. It is possible for the RS-485 port to be
operating at the same time as the RS-232 port is sending data to another location, using either
Acknowledged or Unacknowledged mode (MDC).
RS-232 links can also be made in Unacknowledged mode - the 455U units can effectively
provide a “multi-drop” network for RS232 devices, provided the devices use a communications
protocol that includes addressing and message acknowledgments.
Normally Unacknowledged mode would be used with PLC’s and similar devices.
Acknowledged mode is suitable for point-to-point RS-232 links where the host devices do not
provide addressing or message acknowledgment. Multi-point networks are possible in
Acknowledged mode, however a “master” host device must control connecting and disconnecting
to remote units using AT commands.
It is possible to configure different units in the same system with different operating modes,
however this requires care. A 455U-D unit configured in one mode can act as a repeater for
messages sent between two 455U-D units configured in the other mode, and it is always possible
to send Unacknowledged mode messages to the RS-485 port on a module regardless of the
configuration of the RS-232 port.