485DSS-0812 Manual
3
B&B Electronics Mfg Co Inc – 707 Dayton Rd - PO Box 1040 - Ottawa IL 61350 - Ph 815-433-5100 - Fax 815-433-5104
B&B Electronics – Westlink Commercial Park – Oranmore, Galway, Ireland – Ph +353 91 792444 – Fax +353 91 792445
RS-232 Port
The RS-232 DTE port is an asynchronous port that supports TD
and RD signals. In order to make the proper connections to the RS-
232 port. It is necessary to have a basic understanding of the terms
DCE and DTE. The original design for connecting RS-232 devices
together uses DB25 connectors, and connects a DTE (
D
ata
T
erminal
E
quipment) device to a DCE (
D
ata
C
ommunication
E
quipment)
device. Each device will have inputs on pins that correspond to
outputs on the same pins of the other device. For example, a DTE
device transmits data out on pin 2 and a DCE device receives data in
on pin 2. IBM PC's are DTE devices and modems are DCE devices.
Only TD and RD of the RS-232 port pass through to the RS-485 port
when the 485DSS is ON. The 485DSS raises and lowers the RTS
output signal on the RS-232 port to reflect the connect state of the
port. This signal can notify the RS-232 device to start
communicating to the Host or it can be an alarm output. The Host
can monitor the CTS input line to determine if the RS-232 device is
requesting access to the network. This input line could also be an
alarm input.
NOTE:
If using RTS or CTS lines as alarms the user
may have to design additional circuitry to properly interface to the
alarm circuits. Refer to cable charts in Appendix C for making your
own cables.
Table 1. RS-422/485 Port
Terminal
Block
Signal
Description
RS-422/485
Signal
Direction of
Port
FR GND
Frame Ground
<------>
TD(A)(-)
Transmit Data (A)(-)
Output
TD(B)(+) Transmit Data (B)(+) Output
RD(A)(-) Receive Data (A)(-)
Input
RD(B)(+) Receive Data (B)(+)
Input
GND
Signal Ground
<------>
+12VDC Power Supply
Input
