Filter
Top Products
20
SHORT HAUL MODEM (SHM-FSK)
8. RS-485 Interface
Optional RS-485 modules are available for connection to multiple remote
devices. The following modules are available:
• RS-485 Module 2-Wire, part number MD3317
• RS-485 Module, 4-Wire, part number MD3318
All operating functions and instructions are the same as for the RS-232 full
duplex version, except that the digital interface through the DB25 connector
uses pin 12 as the -DO/RI connection and pin 13 as the +DO/RI connection.
The RS-232 connections (pins 2, 3 and 7) are not functional.
CAUTION
Do not connect anything except an RS-485 signal to positions 12 and 13
on the DB25 or damage to the circuit could occur.
The AE-485 (Auto Enable) circuit contains a special feature that eliminates
the need for a separate enable signal or line to command the 485 transmit
and receive functions. Data will pass through the SHM-FSK’s
RS-485 port transparently in either direction. The SHM-FSKs are operated in
full-duplex point-to-point mode (no carrier control) when using the AE-485
interface. Up to 32 remote RS-485 devices can be multi-dropped off the SHM-
FSK AE-485 port at distances of up to 4000 feet and at data rates of 9600 baud.
A 100-ohm termination resistor should be connected at the ends of the 485
line.