User`s guide

DTR Power Control
The RMX232 radio modem has three states of operation in terms of power
consumption. Maximum power consumption within the radio modem occurs during
data transfer.
A short period after the data transfer has ended the radio modem enters a standby
state whereby power consumption is more than halved. To resume normal data
transfer again the radio modem either sends a wake up message, or receives a
wakeup message, which upon receipt, effectively takes the radio modem out of its
standby state.
A third operating state that places the radio modem into a complete power down state
is achieved by the use of DTR. When DTR is not asserted, the radio modem shuts
down and hence draws very little power. This is ideal for long term battery operation of
remote installations. In this state the radio modem can only be woken by asserting
DTR again.
The use of DTR to control the shutdown state of the radio modem can be enabled or
disabled by the dtr keyword in the command line configurator.
If the connected host has no DTR output signal, then the DTR power control must be
disabled. When operating with DTR power down disabled, it is recommended to use
an external power source to power the radio modem as the internal battery will not last
for extended periods of use.
A word of caution: If the radio modem has DTR power control enabled and is
connected to a serial port that does not have DTR connected, it will not be possible to
wake up or use the radio modem. In this instance, DTR power control must be
disabled.
Operating Modes
The radio modem supports five modes of operation. The first being the default mode,
point-to-point, is a fully controlled data transfer mode using packet acknowledgements
and retries to guaranteed delivery and reliability of data. The second mode is a fully
acknowledged point-to-multipoint mode, with the same reliability features as point-to-
point mode. The third mode is an unacknowledged transfer mode referred to as
broadcast multi-drop mode. The fourth mode of operation is fully acknowledged multi-
master, whereby multiple remote modems can establish a connection with a single
master. The final mode of operation is as a network repeater.
Acknowledged Point-to-Point
This mode of operation is determined by the configuration command keyword
ptpmode being set to ON.
During normal point-to-point operation, packets of data are transferred between only
two Radio Modems. Each Radio Modem pair is configured with a matching site code
and unit address. Only a corresponding modem with an address and site code
matching the destination address of the data packet will accept and process a data
packet and output the serial data.
Before data can be exchanged between a pair of Radio Modems a link must be
established. When a modem has serial data to send it transmits a connect request
message. Either Radio Modem can initiate a connect request when they have data to
send.
User’s Guide Modem Operation Explained 4-5