* The RSFRQ is a non-isolated RS232 to RS485 quad converter/repeater with automatic transmit enable.
* The RSFRQ can be operated from 300-115.2K Baud as a converter and up to 115.2K Baud as a repeater.
* Eliminates the need for software data direction control. Say good-by to RTS and say hello to reliable and collision free data communications.
* Onboard terminal strips & RJ11 connectors allow for easy external connection.
* Common mode transient protection and indicator LEDs are standard.
* Single onboard switching power supply for 9-35VDC operation.
* Units can be cascaded to form very large networks for greater distances and/or greater number of nodes on a network.
RS232 to RS485 or RS485 to RS485 set by onboard jumper.
9-35VDC @ 225-60mA (Max.) or
12-24VAC @ 175-85mA (Max.)
4.0" x 6.6" x 0.9"
Standard Baud Rates:
300, 600, 1200, 2400, 4800, 9600, 19.2K, 38.4K, 57.6K, 76.8K, 115.2K.
6-13.5 total bits (start, data, parity, stop bits), e.g. [N,8,1], [E,7,2], [N,9,2]
The RSFRQ, Automatic Communications Converter/Repeater provides quad non-isolated conversion between RS232/RS485, or it can be used as an quad non-isolated RS485/RS485 repeater. The unit does not require any handshaking signals from the RS232 port of a PC or other host computer, and is intended to operate in 2-wire RS485 applications without any additional control lines. The RSFRQ is generally used in one of two situations:
1) As an RS232 to RS485 converter with automatic transmit enable. In this configuration, the unit is in a receive mode, and any data on any 2-wire RS485 communications lines (if enabled) will be coupled into the receiver data line of the RS232 port of a PC or other device. When the host PC is ready to send data, the start-bit "edge" of the RS232 transmit data line is detected by the RSFRQ and the RS485 transmitters are turned on ("on the fly") for a length of time determined by jumper setting on the unit. The transmitters remains on for one "character" time and then reverts back into a receive mode again. Any number of characters can be transmitted in a string, without introducing any delays between characters. The RSFRQ will stay "in-sync" with the transmitted string and re-trigger on the start-bit of each character in the string. This function is extremely important for making a transparent conversion from RS232 to RS485 without additional control signals, and without having to make changes to existing software. Precise timing is provided without any intervention from a high level operating system such as Windows, OS2, UNIX, Windows 95, etc. The unit can also be interfaced to a modem. The RSFRQ can be used to implement an RS485 "back-bone" or "star" configuration from a host computer with an RS232 port.
2) As an RS485 to RS485 quad repeated with automatic transmit enable. In this configuration, the unit is in a receive mode on all RS485 ports. When data is received on any port (if enabled) the transmitter of the master port will be automatically enabled and data will flow to that side of the interface. The RSFRQ operates as a "true" bi-directional RS485 data repeater without any additional control lines. Multiple units can be cascaded for greater distances and/or greater numbers of remote "nodes" on the network. Jumper selection provides for precise timing and/or re-triggering of any communications string length (see 1).
Observe all normal safety procedures.
1) Use caution when working with or near Mains voltage.
2) Check the relevant site/installation/location drawings before using penetrating manual or power tools which may contact or come close to electrical wiring. Consult with a qualified electrician if there is any uncertainty regarding damage from contact with electrical wiring.
3) Call a qualified electrician to disconnect Mains voltage near power circuits.
4) Use insulated shoes to prevent grounding when working near power circuits.
5) Use protective clothing at hazardous sites or at sites where the use of such clothing is mandatory. In particular be aware of the need for protective hard hats and footwear.
6) Do not install the device in environments in which the local area is subject to dust, grease or vapors which may be flammable, explosive or corrosive.
7) Do not operate the unit in an environment which exceeds the operating specifications for said unit.
8) Use only the correct tool for the intended application.
The Model RSFRQ commu-nications converter/repeater is a flexible AUTOMATIC module for converting full duplex RS232, into half duplex RS485 or for acting as a quad RS485 to RS485 repeater to extend the maximum communications distance and/or to expand the total number of nodes on an RS485 network. The unit is fast, precise, small, automatic, flexible, and intelligent. Say goodby to RTS (Request to Send) timing problems and hello to fast reliable RS485 commu-nications from 300 Baud to 115.2K Baud. Use new or existing software and eliminate delays between characters and response delays from remote slave units. Standard and non-standard Baud rates can be implemented via jumper selection.
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 conver-sion units generally use the RTS (Request 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 command must remain asserted to allow the final character in the string to be transmitted through 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 trans-ceiver has not reverted into the receive mode, the start bit of the first response character and/or the entire 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 half duplex distri-buted 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 RSFRQ quad communications converter/ repeater to save the day. The RSFRQ 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 RSFRQ detects the start bit and places the transceiver 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 between characters is required and no delay is required to receive a response string from a slave device. The RSFRQ controls timing in the microsecond range while the PC can generally only control the RTS line in the several millisecond range. This precise timing insures 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 RSFRQ unit will solve this problem. Simply install jumpers for the Baud rate and the total number of data bits used (1/2 bit resolution), and set additional jumpers to enable the desired number of ports.
An onboard voltage regulator is provided to drive all logic and indicator LEDs. Interfacing to a host computer, such as an IBM compatible PC, is made easy by using an inexpensive 6-wire "telephone" cable and a DB-9F or DB-25F adapter (please specify). 70 onboard jumper options are provided to insure maximum flexibility in a wide variety of applications.
By converting from RS232 to RS485 the user can operate at Baud rates from 300 to 115.2 K and at distances to 4000 feet or more. Multi-drop systems of 128-units can be implemented using the RSFRQ conversion board.
Communications systems using 2-wires can be implemented with provisions for a common ground and shielding. Onboard end of line 120 Ohm termination (DC/AC) is jumper selectable on the board. The "Bullet proof" RS485 link has common mode protection, communications fuses, termination and a jumper selectable biasing network. Seven LED indicators show the data direction flow. The Red LEDs indicates the Transmitter mode while the Green LED indicates the Receiver mode.
RJ-11/12 ("telephone") connectors are provided for "daisy chain" connections of the RS485 TX/RX lines. For applications requiring shielded cable, five onboard 4-pin terminal strips are provided.
Power can be from 9-35VDC or 12-24VAC @ 2W max. A terminal strip is provided 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.
The RSFRQ can be used for two separate functions. These two modes of operation require that the unit be configured differently.
RS232 SERIAL PORT CONNECTIONS: (J27 INSTALLED, J28 REMOVED)
The RSFRQ is connected to the RS232 port of a PC or other host computer via a 1:1, 6-wire "telephone" cable. An onboard RJ-11 connector allows for easy connection at the RS-232 port of the unit. DB9F or DB25F adapters are available for connection to the host computer, or a cable can be constructed using Table 1 below. It should be noted that "hand-shaking" signals are not required for operation; however, pull-up resistors are provided on the RSFRQ as "dummy" signals to the host RS232 port. Also, pin #1 on the RS232/RJ11 connector is indicated by a square pin on the circuit board (note: pin #1 is the opposite of the convention used by the phone company).
TABLE 1 RS232 COMMUNICATIONS INTERFACE
|RX DATA||2||3||5||J1,J2 INSTALLED|
|TX DATA||3||2||4||J1,J2 INSTALLED|
|S GROUND||5||7||3||SIGNAL GROUND PIN|
|DSR||6||6||6||PULL-UP TO +5V|
|RTS||7||4||2||PULL-UP TO +5V (LOAD)|
|CTS||8||5||1||PULL-UP TO +5V|
The RSFRQ is configured at the factory for operation as an RS232 to RS485 converter (mode 1), with communications specification of 9600,N,8,1 (9600 Baud, 1 start bit, 8 data bits, 1 stop bit), RS485 termination enabled (AC), and pins 1&6 of the RS485/RJ11 connectors connected to logic ground. Always remove power when making changes in jumper settings. This is necessary to prevent potential damage to the unit, and to load Baud rate/communications settings into the onboard controller during its power-up sequence. Failure to follow this procedure could result in unsatisfactory operation of the unit. See table 2.
TABLE 2 GENERAL JUMPER SELECTION (J1-J9) (5-CELLS, A,B,C,D,E)
|J1||ENABLE 120 OHM||J1||ENABLE TERMINATION(AC/DC SEE J2)|
|J2||AC/DC||J2||REMOVE FOR AC INSTALL FOR DC|
|J3||POSITIVE BIAS 910||J3||HEAVY POSITIVE BIAS OF 910 OHMS|
|J4||POSITIVE BIAS 2.2K||J4||LIGHT POSITIVE BIAS OF 2.2K OHMS|
|J5||NEGATIVE BIAS 910||J5||HEAVY NEGATIVE BIAS OF 910 OHMS|
|J6||NEGATIVE BIAS 2.2K||J6||LIGHT NEGATIVE BIAS OF 2.2K OHMS|
|J7||NON-INV FUSE SHUNT||J7||INSTALL TO SHUNT THE NON-INVERTING FUSE|
|J8||INVERTING FUSE SHUNT||J8||INSTALL TO SHUNT THE INVERTING FUSE|
|J9||PINS 1-6 TO COMMON||J9||INSTALL FOR RJ11 PINS 1-6 TO LOGIC COMMON|
BAUD RATE SELECTION:
Jumpers J14-21 are used to select the desired Baud rate. When jumpers J14-17 are installed, jumpers J18-J21 are ignored by the onboard controller and the communications specification is set for the factory default of 9600,N,8,1. When changing from the default setting to any other setting (even at 9600 Baud) it is necessary install/remove all jumpers from J14 thru J17 (all Baud Rate and Data Bit jumpers). Always remove power when making changes in jumper settings. This is necessary to prevent potential damage to the unit, and to load Baud rate/communications settings into the onboard controller during its power-up sequence. Failure to follow this procedure could result in unsatisfactory operation of the unit. See table 3. Note: Special driver required.
TABLE 3 BAUD RATE SELECTION JUMPERS (J14-J17)
|38400||REMOVE||INSTALL||INSTALL||INSTALL||SPEED OPTION REQUIRED|
|57600||INSTALL||REMOVE||REMOVE||REMOVE||SPEED OPTION REQUIRED|
|76800||INSTALL||REMOVE||REMOVE||INSTALL||SPEED OPTION REQUIRED|
|115200||INSTALL||REMOVE||INSTALL||REMOVE||SPEED OPTION REQUIRED|
9600* Is the factory setting for 9600,N,8,1 with jumpers J18 thru J21 ignored. Power down to make changes.
Jumpers J18 thru J21 are used to select the desired communications specification (total data bits). The start bit is always present and counts as one bit. The parity bit, if N (none) does not count as a bit; however, if the parity is P (even, odd, mark, space) then add one to the total number of bits count. Data bits can range from a minimum of 4 up to a maximum of 11 if parity is N. One, two or more stop bits can be selected as long as 13-1/2 total bits are not exceeded. See table 4.
TABLE 4 TOTAL NUMBER OF BITS (J18-21), (START, PARITY, DATA, STOP)
|J18||J19||J20||J21||NOTES AND EXAMPLES:|
|6||REMOVE||REMOVE||REMOVE||REMOVE||MINIMUM TOTAL BITS|
|9-1/2||REMOVE||INSTALL||INSTALL||INSTALL||N,8,1/2 FOR FAST MICRO.|
|13-1/2||INSTALL||INSTALL||INSTALL||INSTALL||MAXIMUM TOTAL BITS|
N=No Parity (Bit = 0), P=Parity (even, odd, mark, space, Bit = 1)
It is generally not desirable to add extra stop bits because "data collisions" could occur. A half-bit (time) resolution is provided because many fast microprocessor units will respond after detecting the center of the final stop bit. The half-bit timing allows the RSFRQ to revert back into a receive state in fast systems without the need to introduce system delays to avoid "data collisions." With the proper jumper settings, the RSFRQ is capable of error free operation, at very high Baud rates, without introducing additional system time delays. Erratic or no data communications could indicate that the jumper setting are incorrect or that the power was not removed when changing jumper settings.
TABLE 5 MODE JUMPERS (J22-J34)
|J22||ENABLE CELL A||J22||CELL A ENABLED IF JUMPER IS INSTALLED|
|J23||ENABLE CELL B||J23||CELL B ENABLED IF JUMPER IS INSTALLED|
|J24||ENABLE CELL C||J24||CELL C ENABLED IF JUMPER IS INSTALLED|
|J25||ENABLE CELL D||J25||CELL D ENABLED IF JUMPER IS INSTALLED|
|J26||ENABLE CELL E||J26||GENERAL ENABLE (MUST BE INSTALLED)|
|J27||ENABLE RS-232 MODE||J28||J28||ENABLE RS232 CONVERTER MODE|
|J28||ENABLE RS-485 MODE||J28||J27||ENABLE RS485 REPEATER MODE|
|J29-J31||RESERVED JUMPERS||ALL||RESERVED JUMPERS FOR EXPANSION (NOT USED)|
|J32- J34||RESERVED POWER||ALL||RESERVED POWER FOR EXPANSION (NOT USED)|
Seven LED indicators show the status of the RSFRQ. The Green LED marked PWR indicates power is applied. The 2 Red LEDs monitor the RS232/RS485 TX status, while the 4 Green LEDs monitor the RS485 RX status from cells A,B,C, and D. When power is applied to the unit, only the Green PWR LED should come on to indicate a ready condition. When communications is initiated from the primary side (cell E) of the interface (RS232/RS485) one of the two Red LED near the center of the board will come on indicating that data was received on the primary (cell E) side of the interface and transmitted out the secondary RS485 side (cells A,B,C,D) of the interface. Data from the secondary side will cause one of the Green LEDs near the center of the circuit board to come on while data is present. Mode jumpers can modify the operation of the LED indicators. See Mode Jumper (Table 5) above.
The RSFRQ can be operated from 12-35VDC or from 12-24VAC; however, when operating at power supply voltages near the maximum value precautions should be taken to insure that transients will not cause the maximum rating to be exceeded. Power can be supplied via the circular power jack (2.1mm center pin), or the power terminal strip. Polarity is not important because of onboard full-wave bridge circuitry. It is normally best to operate the RSFRQ from a separate transformer isolated power supply to avoid grounding problems and sneak paths through the power supply bridge circuitry. If a common supply is used, connect the positive side of the supply to one of the power terminal strip locations, and the negative side (common) to one of the "C" terminal strip locations on the RS485 terminal strip near the letter "E" cell.
This mode of operation is very similar to the converter mode of operation; however, jumper J27 is removed and J28 is installed. All other aspects of operation remain the same, and there are no special driver chips required for operation above 19,200 Baud.
R.E. Smith, 4311 R. E. Smith Dr., West Chester, Ohio 45069
513-874-4796 Phone, 513-874-1236 Fax., rs485.com