The RSFC2 Converter - Detailed Information

When making the conversion from a PC full duplex RS232 serial port to a half duplex RS485 two-wire system, many potential timing problems can arise. NON-AUTOMATIC conversion units generally use the RTS (Requst To Send) signal to control the direction of data flow. A "critical" data timing window" occurs when the PC transmits the final character in a command string to a slave device on an RS485 "bus."

When the final command character is transmitted from the PC, the RTS comand must remain asserted to allow the final character in the string to be transmitted throught the RS485 transceiver. Once the final character has cleared the transmitter, the slave device will often respond within a matter of microseconds to milliseconds. If the transceiver has not reverted into the receive mode, the start-bit of the first several characters of a response string can be lost.

In general, the PC is just not capable of performing the precise timing required for high-speed duplex distributed systems. Even when the PC is fast enough to control the timing, custom software is often required to make the full-duplex to half-duplex transition. If custom software is not available, the choices of external devices that can be interfaced is severely limited.

Enter the Model RSFC2 communications conversion controller to save the day. The RSFC2 controls the RS485 transceiver on a character-by-character basis to resolve the "critical data timing window" and other problems when making the full-duplex to half-duplex transition. The unit remains in a receive mode until a character is transmitted from the PC. The RSFC2 detects the start bit and places the tranceiver in a transmit mode for one character time and then enters the receive mode again. Multiple characters from the PC simply cause the unit to enter the transmit mode for the time required. No delay betweeen characters is required to receive a response string from a slave device. The RSFC2 controls timing in the millisecond range. This precise timing ensures reliable data communications. Many of our customers tell us that they have worked 40 to 60 hours trying to resolve this timing conflict without success. Installing the Model RSFC2 unit will solve this problem. Simply install jumpers for the baud rate and the total number of data bits used (½ bit resolution).

An onboard voltage regulator is provided to drive all logic and indicator LED's. Interfacing to a host computer, such as an IBM compatible PC, is made esy by using an inexpensive 2/6-wire "telephone" cable and a DB-9F or DB-25F adapter (please specify). Twenty-three on-board jumper options are provided to ensure maximum flexibility in a wide variety of applications.

By converting from RS-232 to RS-485, the user can operate at Baud rates from 300 to 115.2k and at distances to 4000 feet or more. Multi-drop systems of 32 units can be implemented using the RSFC2 conversion board.

Communications systems using 2-wires can be implemented with provisions for a common ground and shielding. On-board end of line 120 Ohm termination or 120 Ohm in series with 0.1uf is jumper selectable on the board. The "Bullet Proof" RS485 link has common mode protection, automatic fuses, AC/DC termination and jumper-selectable network biasing. An RX enable jumper is provided for echo/test mode. TWo LED indicaors show the data direction flow. The Red LED indicates the Transmitter activity while the Green LED indicates the Receiver activity.

RJ-11/12 ("telephone") connectors are provided for "daisy chain" connections of the RS485 TX/RX lines. For applications requiring shielded cable, an on-board 4-pin terminal strip is provided. An optically isolated AUTOMATIC unit (Model RSFR, RS232 to RS485) is also available and can be used as an AUTOMATIC RS485 to RS485 repeater.

Power can be from 9-35VDC or 12-24VAC @ 100mA. An optional terminal strip is available for transformer connections.

WARNING: Do NOT connect this device to a telephone system under any circumstances. Damage could result to the circuit board and/or your telephone system.

Model RSFC2 for operation to 19.2k Baud	$89.00
Speed Option (115.2k)	2.00
Enclosure Option	10.00
DB9F or DB25F cable	7.50
Power Supply	7.50
Power terminal strip	3.00

Please call us at: 513-874-4796