DGH Corporation, A1000/220V, RS-232/RS-485 Communications Converter, 220V
Features:
- Completely transparent to host software
- No external flow control signals required
- Optically-isolated bidirectional data flow
- Standard baud rates: 300 to 115K baud
- Automatic internal RS-485 bus supervision
- Networking up to 4,000 feet
- Transient suppression on RS-485 data lines
- Internal jumper selectable termination resistors
- Internal 1KOm biasing resistors on RS-485 data lines
The A1000 series isolated RS-232 to RS-485 serial communication converters will convert RS-232 signals to the correct electrical signal levels required by RS-485 devices. RS-485 is recommended in applications where many DGH modules, or other addressable devices, must be connected to a host computer and communicate over a long distance. The A1000 will allow communications bus lengths up to 4,000 feet using baud rates up to 115.2K baud on one twisted pair of wires.
Applications requiring data transmission over 4,000 feet can use another A1000 as an RS-485 repeater. Used as an RS-485 repeater, the A1000 will re-amplify and re-transmit the RS-485 signals another 4,000 feet. Simply connect another A1000 to the end of an existing communications line to extend the data transmission distance. The A1000 repeater connection also required when connecting more than 32 devices to an RS-485 communications line. The standard requires a repeater after every 32 connected devices.
The A1000 converters automatically control their internal RS-485 driver receive/transmit direction without the need of external handshaking signals from the host computer. Once the host computer begins to transmit data, the A2000 will automatically enable the internal RS-485 driver for one-character time at the selected baud rate and then return the driver to receive mode. Using this automated technique host software written for half-duplex RS-232 applications may be used without modification.
Each A1000 also contains DIP switch selectable RS-485 termination and biasing resistors on the rear panel of each device. The RS-485 standard is highly immune to noise when each data line is properly biased and terminated. The DIP switch selectable pull-up and pull-down biasing resistors and termination resistors are provided for proper biasing of the communication line.
For more information, please see 
Data Sheet
