Installation
20
User’s Manual - SM19202 Fast Poll Modem
S2- 9
−−−−
Forced RTS ON (Constant RTS)
S2-9 ON = Force the modem’s internal RTS to on. It also force the modem to turn
on CTS and the transmit carrier.
S2-9 OFF = Internal RTS is controlled by the RTU (default)
Switch 2-9 will force the modem to turn on its internal RTS, CTS and transmit carrier
continuously, allowing the RTU and DTE to operate with the modem without supplying RTS
signal. This is primary used by DTE’s or RTU’s that support only TD, RD and SG signals.
Forced RTS on option is typically used for point-to-point connections between two RTUs or
modems. For multi-point applications, the salve modems should not use this option.
S2- 10
−−−−
Re-Train Request Enabled
When the SM19202FP modems are operating in high-speed polling modes, the modem’s
receivers require a special training pattern from the remote transmit modem to synchronize
the receive timing before data can be received. The SM19202FP will only send out a training
pattern when the transmit modem’s RTS is raised from the OFF to ON state (i.e. Switched
Carrier mode). However, if the modems are configured in Constant Carrier mode, or the
RTS is ON continuously by the DIP switches, no training pattern will be sent from the
transmit modems. When in configurations where constant carrier is received at the
modem’s receiver, there is a possibility that the modem might lose synchronization due to
transmission line interferences such as line hits, line drop-outs, or power outage conditions.
In order to regain synchronization at the receiver, the SM19202FP modem implements a re-
train algorithm which allows the receiving modem to send out a re-train request to the
remote modem for re-train and re-gain synchronization. This option is most useful for the
modem to operate at 19200 bps and constant carrier or constant RTS modes.
S2-10 ON = Re-Train Request is Enabled (for 19,200 bps only)
S2-10 OFF = Re-Train Request is Disabled (default)
S3- 1 and S3-2
−−−−
RS-232 or RS-485 Interface Select
The SM19202FP standalone modem support either RS-232/V24 or RS-485 4-wire or RS-
485 2-wire operation. To select the interface standards to match you RTU, configure S3-1
and S3-2 as following:
•
RS-232/V.24:
S3-1 = OFF, S3-2 = OFF
•
RS-485, 4-wire:
S3-1 = ON,
S3-2 = OFF
•
RS-485, 2-wire:
S3-1 = OFF, S3-2 = ON
