DATA-LINC GROUP
7
MDL500 User Guide
PN 161-10003-002B
rev 8/03
Carrier Detect
The Carrier Detect signal to the RS232 connector is enabled or disabled by Jumper Matrix P3. The MDL units are shipped
with the Carrier Detect enabled (jumper on).
Chassis Ground
Chassis ground can be connected to signal ground via Jumper P5. This is generally not recommended. A separate chassis
ground wire may be connected to the MDL’s metal enclosure by means of any of the cover mounting screws as desired to
avoid a possible shock hazard.
Half-Duplex Operation/Carrier Control
The MDL500 can be operated in multi-drop/half-duplex mode by controlling the transmitter’s carrier on/off using external
signals. The most common external carrier control signal is through the RS232 port RTS line (pin 4). Jumper P4, A-B,
selects this line. When an external RTS logic high is asserted, the MDL carrier is turned on, and a logic low or ground,
turns the carrier off. The MDL RTS line is biased low so that if the RS232 cable is disconnected or the external controlling
device is turned off, the carrier will go off. Selecting jumper P4, B-C, turns the transmitter on and blocks RTS carrier control.
The B-C setting is used in full-duplex operation. Usually only the Remote units have their carriers controlled by the devices
they are connected to (setting A-B). The Master unit’s carrier is left on all the time (setting B-C). (There is no interference
since the Master and Remote carrier frequencies are different.) The factory setting for both MDL Masters and Remotes is
P4, B-C, for full or half-duplex, point-to-point operation.