Lecnet Computer Interface - Lectrosonics UDR200C Operating And Troubleshooting Manual

Lectrosonics' LecNet system is a unique implementation of
standard RS-232 serial communications. Since it is compat-
ible with RS-232 serial ports found on all PCs, no extra inter-
face cards are necessary to add computer control to your
LecNet equipment. The figure below shows a representation
of a LecNet setup. Unlike standard RS-232 equipment, where
one serial port connects to only one device, as many as 127
LecNet devices may be simultaneously connected to a single
serial port.
As the figure shows, LecNet devices can always receive
information from the host. In this way, each LecNet device
"listens" for its unique network address "broadcast" from the
host PC. When a device "hears" its address, it closes its
Device Tx switch to reply to the host. The Device Tx switch is
held closed until the data exchange with the host is complete.
The device then opens its Device Tx switch. In this way,
device contention is avoided. Each LecNet device must have
a unique address between 128 and 254. Any device address
is reassignable using the LecNet Master Pro application (sup-
plied free with every LecNet device).
The LecNet runs at a fixed rate of 9600 bps, which is not user
adjustable. This is fast enough to provide quasi-real time
response to the control panels while insuring reliable commu-
nications over reasonable distances (100 feet from host to
LecNet device). The serial communications parameters used
are 8 data bits, no parity, 1 stop bit.
LecNet HARDWARE HINTS
Connecting LecNet devices to a host using the LecNet is
straightforward. Using the special LecNet RS-232 cable
(Lectrosonics Part #21529), simply connect Com1, 2, 3 or 4 on
the host to the LecNet 3.5mm input on one of the LecNet
devices. If a custom length cable is necessary, the figure to
the right shows the cable connection schematic. The host-to-
device connection assumes that multiple LecNet devices (if
more than one are used) are interconnected using the 8 pin
expansion cable (Lectrosonics Part #21551).
20
TM
LecNet COMPUTER INTERFACE
Host TX
Host
RX Device
Device
RX TX
Device Device
Device
RX TX
RX
While Lectrosonics has made every effort to make the serial
communications software as compatible as possible with a
wide range of serial ports, some serial ports are not well
behaved. Some problems occur with older serial ports, be-
cause they may not be reliable at 9600 bps or higher. Soft-
ware is available (from Norton, for example) which will test
serial ports and determine the highest reliable data rate.
In addition, Windows video drivers sometimes interfere with
com port operation. For example, the custom video driver
supplied with the Toshiba 1900/1910 series laptop computers
will crash the com port when it is used for LecNet operation.
The fix for this situation is simply to use the generic VGA video
driver (chosen from the Windows Setup application). Watch
for video driver interactions any time a nonstandard video
driver is used.
Device
TX
LecNet Device to PC
S
R
3.5MM
T
Stereo Plug
Wiring Diagram, 9 Pin D-Sub
Tip LecNet Device Transmit
Ring LecNet Device Receive
Sleeve Gnd
LecNet Port
Wiring Diagram, 25 Pin D-Sub
Tip LecNet Device Transmit
Ring LecNet Device Receive
Sleeve Gnd
LecNet Port
9 or 25 Pin Female
D-Subminiature
N/C CD 1
RX 2
TX 3
Host
DTR
4
Serial
Gnd
5
Port
DSR 6
(PC)
RTS 7
CTS 8
N/C RI 9
RX 3
TX 2
Sig Gnd 7
Host
Chassis Gnd 1
Serial
RTS 4
Port
CTS (PC)
5
DSR 6
DTR 20