Instructions

UM-0085-B09 DT80 Range User Manual Page 203
RG
Powering the DT80’s Modem
If required, the DT80 can control power to the modem, so that it can be powered down under program control when not
in use.
This can be done using either:
• the RELAY output – see DO5 – Latching Relay Output (P336); use 1RELAY=1 to switch on modem power,
1RELAY=0 to turn off, or
• one of the digital outputs 1D-4D driving an external relay – see DO1 – Driving a Relay (P335); use
1DSO=0 to
switch modem power on,
1DSO=1 to turn off, or
• the 12V power output (DT80/ 81 Series 2 and DT85 only), provided that the modem draws no more than
150mA.The DT80 Series 4 has the 12V power output capabilities of up to 300mA.
Automatic Modem Power-Down Reset
The DT80 provides an additional feature where the modem can be automatically reset (by removing and re-applying
power) if it appears to be unresponsive – that is, it has been off-line (i.e. not connected to the remote modem) for a long
period of time (12 hours, by default – set this using the
MAX_CD_IDLE profile key).
To enable this feature, send one of the following
PROFILE commands:
• If the modem is powered from one of the DT80’s digital output channels n (where n =
1 to 4), send the
command
PROFILE HOST_MODEM EXT_POWER_SWITCH=nDSO
• If the modem is powered via the DT80’s relay channel, send the command
PROFILE HOST_MODEM EXT_POWER_SWITCH=1RELAY
• If the modem is powered via the DT85's 12V power output, send the command
PROFILE HOST_MODEM EXT_POWER_SWITCH=PWR12V
• If the modem is not powered by either of the above, send the command
PROFILE HOST_MODEM EXT_POWER_SWITCH=NONE
to disable the feature.
From then on, the DT80 will automatically cycle the modem power if it detects it to be unresponsive. It will then send the
configured modem initialisation string.
Modem Communications Operation
Dialling In
The DT80 does not communicate via the RS232 host port unless it determines that a call has been established between
itself and a host. When a modem is attached (DSR active) , the DT80 monitors the DCD signal to determine when it can
transmit data and status information, and receive commands.
• When DCD is active the DT80 accepts commands, and returns data and status information – exactly as it would
for a direct connection.
• When DCD is inactive the DT80 ignores any received characters and does not transmit data or status
information.
This behaviour ensures that any rubbish characters received outside of a call are ignored, and that the DT80 does not
send characters to the modem that the modem may interpret as commands to switch into a different operating state.
Dialling Out
The DT80 can also initiate an outgoing modem call, which would typically be done in response to an alarm.
 SETDIALOUTNUMBER Command
Send the command
SETDIALOUTNUMBER"digits"
to the DT80 to specify the telephone number to be dialled by the
DIAL command to establish a connection to the host
computer.
 DIAL Command
The DIAL command causes the DT80 to instruct its modem to dial out to the telephone number specified by
SETDIALOUTNUMBER. If a call cannot be placed for any reason, the command is ignored. This is often used as an
alarm action command to cause the DT80 to dial out when an alarm condition arises.