User manual

905U-D Radio Modem User Manual
Man_905D_1.10.doc Page 26
There is a special configuration of controlled mode which provides a 5msec lead-in time for fast
operation (see below). With the fast operation, the time to transmit 20 bytes at 19200 baud is
less than 20 msec.
There are several configurations for controlled mode:
3.6.1 Auto-Connect Controlled Mode
Auto-connect mode is similar to “fixed line” modem operation. The master unit wants to
connect to only one slave address. Normally the slave address is preconfigured. On power up,
the master unit continuously tries to connect to the slave address. The slave unit, on power up,
does not try to connect but waits for a connect message. Once a connection is made, the DCD
status at both ends is set and data can be transferred in either direction. If there is no data transfer
within the preconfigured “link check” time, the master will send a connect message to check the
communications link.
The connection will be broken if a communication failure occurs, or if one of the hosts issues a
“disconnect” AT command (although this would be unusual for this mode). When the master is
disconnected, it will continuously try to connect to its auto-connect address.
Up to five repeater addresses may be configured as part of the auto-connect address. That is, up
to 5 intermediate modules can act as repeaters between the master and slave modules.
3.6.2 Low Power Auto-Connect Mode
For special installations, the 905U-D may be operated in a low power condition where it
switches off its receiver - power consumption is reduced to approx 30% of normal. The low
power condition will occur if the 905U-D is configured for auto-connect mode AND if the low
power mode feature is configured. The DTR signal on the RS232 port will control switching
between low power and normal operation. When DTR is “low”, the module will change to low
power operation, reset any connected link and switch off its receiver. When DTR goes “high”,
the module will revert to normal operation and will auto-connect to its slave address.
The use of this low power operation may be applicable in remote locations where there is a
limited power supply such as solar panels. In this situation, the DTR signal from the host device
is used to “wake-up” the 905U-D unit. The 905U-D unit will then operate normally until the
DTR signal is reset by the host device.
3.6.3 Single-Connect Controlled Mode
Single-connect is similar to a dial-up modem. In this mode, the module will only make one
attempt to connect to a destination address. A host device will issue a connect AT command,
and the module will send a connect message to the destination address. If the destination module
responds, then the link is connected and the DCD status is set. If the destination module does
not respond, then the link is not established and no data can be transferred. The module will not
attempt to reconnect again until it receives another connect command from its host.
The link is normally disconnected by the host issuing a disconnect command. In this mode, it is
normal for a host to connect and disconnect to several slave modules using AT commands. A
common example is a PC polling several analyzers or dataloggers. The PC connects to a remote
station one at a time, transfers data, disconnects and connects to the next station.