Lectrosonics UDR300c User Manual download pdf (Page 20)

LecNet

COMPUTER INTERFACE

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

Host

Host TX

Device

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).

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.

LecNet Device to PC

3.5MM

9 or 25 Pin Female

Stereo Plug D-Subminiature

Wiring Diagram, 9 Pin D-Sub

N/C

Tip

LecNet Device Transmit

Ring

LecNet Device Receive

Host

Sleeve

Gnd

DTR

Serial

Gnd

LecNet Port

Port

DSR

(PC)

RTS

CTS

N/C

Wiring Diagram, 25 Pin D-Sub

LecNet Port

LecNet Device Transmit

LecNet Device Receive

Gnd

Sig Gnd

Chassis Gnd

RTS

CTS

Ring

Tip

Sleeve

Host

Serial

Port

(PC)

DSR

DTR

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Lectrosonics UDR300c User Manual Page 20

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