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HIGHLIGHTS

OVERVIEW

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).

SAFETY

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.

INSTALLATION

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

JUMPER SETTINGS:

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)

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)

9600* Is the factory setting for 9600,N,8,1 with jumpers J18 thru J21 ignored. Power down to make changes.

COMMUNICATIONS SPECIFICATION:

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)

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)

LED INDICATORS:

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.

POWER SUPPLY:

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.