B&B Electronics 485LPCOR - Datasheet - Manual (Page 2)

485LPCOR-0812 -2/2
© 2003 by B&B Electronics. All rights reserved.
www.bb-elec.com [email protected] [email protected]
International Office: 707 Dayton Road PO Box 1040 Ottawa, IL 61350 USA 815-433-5100 Fax 433-5104
European Office: Westlink Commercial Park Oranmore Co. Galway Ireland +353 91 792444 Fax +353 91 792445
PR
O
D
U
C
T
INF
ORM
A
TIO
N
B
&
B
ELE
C
T
R
ON
ICS
Pin one is also connected straight through on the 485LPCOR from the RS-232 side to the RS-485 side so that the
shield can be passed through to earth ground if desired. It is recommended that shielded cable be used and that the
shield be connected to earth ground at one point in the system. See B&B Electronics’ RS-422/RS-485 Application Note
for further information on shielding.
Although the 485LPCOR uses the handshake lines to power
the converter, no handshaking is required to control the RS-
485 driver. The RS-485 driver is automatically enabled during
each spacing state on the RS-232 side. During the marking
or idle state, the RS-485 driver is disabled and the data lines
are held in the marking state by the 4.7K ohm pull-up and
pull-down resistors. The value of these resistors may need to
be changed to a different value when termination is used in
order to maintain the proper DC bias during the idle state.
See B&B Electronics’ RS-422/RS-485 Application Note for
more information on termination and DC biasing of an RS-
485 network.
The 485LPCOR has an internal connection to prevent data
transmitted from the RS-232 port from being echoed back to
the RS-232 port. The connection can be cut to have the
receiver always enabled. (See Figure 1.) After the connection
is cut, a jumper wire from pin 18 to pin 21 can be installed to disable the receiver during transmission.