MAN0847-01
21 MAR 2007
PAGE 1
No part of this publication may be reproduced without the prior agreement and written permission of Horner APG, Inc.
Information in this document is subject to change without notice.
Introduction:
The HE500232485 is a compact, lightweight and reliable RS232 to RS485 converter, which provides
RS485 half-duplex (2-wire) multi-drop functionality to OCS devices that only support RS232
communications (Mini, OCS100, OCS200). The HE500232485 may also be used to provide RS232 to
RS485 conversion for other devices provided they assert RTS handshaking when RS485 transmission is
required and that handshake line is connected to the converter’s RS232 CTS line.
RS-232 is a point-to-point serial communications standard that defines the electrical and mechanical
details of the interface between Data Terminal Equipment (DTE) and Data Communications Equipment
(DCE). Compared with newer standards RS-232 is limited in terms of data rate, maximum distance and
noise immunity. For longer distances, higher speeds, more noise immunity and the need for multi-drop
connections, conversion to RS-485 is recommended.
Connections:
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diagram
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RS232 -
direct or through a RS232 cable to a DCE DB9 connector.
RS485 -
connect the RS485 data lines to the D+ and D- terminals (observing polarity). Note
that the communications common may be connected to the 0V terminal; however,
since converter is not isolated, standard practices should be applied to avoid ground
loops.
Power -
connect 12-24VDC (100mA max) to the V+ and 0V terminals (observing polarity).
Termination –
when the pin jumper is installed (board side opposite terminal connections),
internal termination resistance (120ohm) is provided.
Cables:
The HE500232485’s RS232 connection (DB-9P) is a wired as a DTE configuration, which allows for direct
connection to OCS device’s RS232 programming/communication ports. If cabling is required between
the HE500232485 and an OCS, it must be straight through and pass the CTS handshake signal as well
as the data lines.
When connecting the HE500232485 to another DTE device (such as a PC) a ‘null modem’ or crossover
cable is required (which must also pass the DTE device’s RTS handshake output to the HE500232485’s
CTS handshake input)
The RS-232 standard suggests operation is possible at about 20 kbps over distances of 50 feet,
depending on grounding and noise considerations. Over short distances, RS-232 is sometimes operated
at rates as high as 115.2 kbps. Several hundred feet is possible at data rates of 9600 bps or lower.
OCS RS-232 to RS485 Serial
Adapter
HE500232485
