Model 65A

RS-232 to Current Loop Converter

 

Reference Manual

0315-0261 Rev. B

 

Printed 05.22.02


Table of Contents

1.0 General Description
1.1 DataSpy Feature 
2.0 Specifications
Interface 
Connectors 
Switches 
Indicators
Power
Size
Environment 

3.0 Installation
3.1 Digital Interface
3.2 Current Loop

4.0 Operation
5.0 Troubleshooting
6.0 Connector Pin Assignments
7.0 Power
8.0 Help

1.0 General Description

The Model 65A is a small, versatile, RS-232 to Current Loop Converter for use with computer peripherals such as teletypes or CRT terminals that require interfacing via 20-mA (or 60-mA) current loops.

The Model 65A includes switch selection of all operating modes. The switchable parameters include loop type, active or passive, and transmission protocol (half or full duplex). An I/O selection switch is included to allow both DTE and DCE devices to be accommodated (e.g., reversing Pins 2 and 3 of the RS-232 connector).

The Model 65A is directly interfaceable to standard teletypes and 20-mA drives. It also accepts 20-mA or 60-mA loop currents. Both units operate from DC to 9.6 kbps. In the passive mode, the units provide total electrical isolation between devices.
 

1.1 DataSpy Feature

Your new Telebyte product incorporates the Patent Pending DataSpy feature - an LCD display designed to assist in the initial installation and check out and to act as a performance monitor. In the event of a system problem, it provides information about the status of the local link.
 


Figure 1: LCD display
 

The Telebyte logo displayed on the LCD screen indicates that the unit is powered (see Figure 1). For power-stealing devices such as a modem, it is an indication that sufficient power is being applied to operate the device. The LCD display uses less than 1 mW of power.

The data display on the LCD consists of graphical representations for TD (Transmit Data) and RD (Receive Data). Each of these signals is displayed as a bit change waveform would appear on an oscilloscope. Ordinarily, TD and RD are low or a minus voltage in the quiescent state. When data is transmitted, the transmit signal is brought high to a positive voltage. These two signal states are displayed on the LCD by either a low segment or a high segment. The low segment represents the negative voltage (the mark condition) while the upper segment represents a positive voltage (the space condition). The vertical bar connecting the lower segment to the upper segment is always on when power is applied. If the transmit signal is in the quiescent state (continuously low) only the lower segment is illuminated. This is an indication of a constant negative state. If the transmit or receive inputs to the device are streaming (in the positive mode continuously) the LCD display shows the vertical segment and the upper segments only. For cases where there is valid data transmission, both the upper and lower segments are displayed simultaneously. A variation in display intensity between lower and upper segments gives the user a perception of the amount of data being transmitted.
 


Figure 2: Block diagram.
  

The LCD display also presents the status of the following control signals: CTS, RTS, DSR, DCD, and DTR. These signals are displayed as mnemonic symbols composed of three letters - each on the bottom line of the display. The presence of the three-letter mnemonic indicates that the respective control signal is high or positive. If the control signal is negative, the three-letter mnemonic is not displayed. For most full-duplex data-only modems, CTS and RTS are connected together while DSR, DCD, and DTR are connected together. For hand-shaking modems there is a relationship between various control signals on both ends of the link. This relationship is dependent upon which control signals are utilized. The DataSpy LCD display helps to verify correct operation.
 

2.0 Specifications

Interface

Conforms to RS-232 and CCITT V.24 specifications. Pins 2 and 3 (Transmit and Receive Data) are switch selectable (reversible). Pin 7 is Signal Ground.

Connectors

RS-232; DB-25M

Current Loop

Five-position screw terminal

Switches

DCE/DTE: Allows selection of I/O lines for interfacing to a modem or a terminal type device.

Half/Full Duplex: Allows selection of either non-simultaneous, two-way transmission without local echo.

Active/Passive: Allows selection of power source (current) for loop operation. Active utilizes internal power for operation whereas Passive requires the user to provide a power source in the external loop. The transmitter and receiver can be individually configured for active or passive.
 

Indicators

LCD display for data, five control signals and power.

Power

110 V, 60 Hz or 220 V, 50 Hz (optional)

Size

2 in W x 4.15 in L x .79 in H

(50.8 mm x 105.4 mm x 20.1 mm)

Environment

0° to 50° C, 5% to 95% relative humidity, non-condensing

 

3.0 Installation

3.1 Digital Interface

The digital interface for the Model 65A converter is a male DB-25, 25-pin connector.

3.2 Current Loop

The current loop interface is a variable depending on the type of device being interfaced and whether a "floating" interface is required. Four typical installations are described in the following text. This should cover virtually all cases.

The five connection points on the Model 65A are K+, K-, G, C+, and C. The K contacts are output connections whereas the C contacts are input connections. G is Signal Ground.
 
 

1. Half Duplex - Active Loop


 
Switch Settings:
 
DTE/DCE - As Required 
Half/Full Duplex - Half Duplex 
Active/Passive - Active
 

2. Half Duplex - Passive Loop

 

Switch Settings:

DTE/DCE - As Required
Half/Full Duplex - Half Duplex
Active/Passive - Passive
 

3. Full Duplex - Active Loop


 
Switch Settings:
DTE/DCE - As Required
Half/Full Duplex - Full Duplex
Active/Passive - Active
 

4. Full Duplex - Passive Loop


 
Switch Settings:
DTE/DCE - As Required
Half/Full Duplex - Full Duplex
Active/Passive - Passive
 

The Model 65A can be configured to operate in either half or full duplex and the transmitter and receiver can operate as either active or passive.


 
 

4.0 Operation

The Model 65A is supplied with a switch that allows the reversing of Pins 2 and 3 of the RS-232 connector. When the switch is in the DTE position, Pin 2 of the EIA connector is an output (transmit-to-host device). Thus, Pin 3 is input. When the switch is reversed to the DCE position, the connectors are reversed (Pin 2 is an input and Pin 3 is an output). When interfacing to a CRT terminal, the switch should be set to DCE.

After the above selection has been made, the Half/Full and Active/Passive switches must be set. Refer to section 3.0, "Installation" to determine the configuration required and set the Duplex and Loop switches accordingly.

The K connections for the converters are outputs to drive signals of the Model 65A. K+ is the collector of the transistor whereas K- is the emitter of that transistor. In the Passive mode, the transistor is floating; the user must supply a source of power. In the Active mode, the Model 65A provides a positive voltage (approximately +12 V) through a 560-W, ½W, resistor to the K+. Collector, contact and current are then available at the K- contact.
 

The C connections on the converters represent the inputs to the diode of an opto-coupler. The C+ connection is the anode of the diode and the C- contact is the cathode of the diode. Regardless of the loop mode selected above, the Half-Duplex mode that connects the emitter of the output drive transistor (K- contact) to the anode of the opto-coupler diode is uncommitted. There is a 33-W resistor in series with the cathode of the opto-coupler diode.
 
When the Model 65A is in the Active mode and set for Full Duplex, the anode of the opto-coupler diode is connected to a positive voltage through a 560-W, ½-W resistor (C+ to +12 V through 560-W), and current is available at the C- contact.
 

5.0 Troubleshooting

The following is a list of problems that may arise during the installation and suggested reasons for those problems.

Problem

The data received is garbled.

Suggested Reason:

a) The DTE/DCE switches are not set properly (see section 4.0, "Operation"). 
 
b) The equipment the Model 65A is connected to does not have its Communication parameters set
 the same as the Model 65A. 
 
c) One of the four wires is broken.
 

Problem:

No data is received.

Suggested Reason:  
a) The customer equipment is not connected to the Model 65A.
 
b) The DTE/DCE switches are not set properly (see section 4.0, "Operation"). 
 
c) One or more wires between the modems are open. 
 
d) The link connection exceeds the maximum distance specified. Individual converter performance can be verified if the device to which the converter is attached is capable of operation in the Non-Echo mode. In this mode, the terminal generates data from its keyboard but data is not displayed until it is received at its port.

The converter may now be tested by providing the "loopback" connections as follows:

Jumper K- to C+
Jumper C- to G

For this test set the switches as follows:

DTE/DCE: DCE
Half/Full Duplex: Half
Active/Passive: Active - Transmit; Passive - Receive

If the converter is functioning correctly any data entered on the keyboard of the terminal appears on the screen.
 
 

6.0 Connector Pin Assignments

Pin

EIA

CCITT

Name

 

2

BA

103

Transmit Data

*

3

BB

104

Receive Data

*

5

CB

106

Clear to Send

**

6

CC

107

Data Set Ready

**

7

AB

102

Signal Ground

Gnd

8

CF

109

Data Carrier Detect

**

 

* These signals can be reversed using the selector switch.
** Connected together and to + voltage.
 

7.0 Power

The Model 65A is powered by a small, wall-mounted power supply that supplies 12 VDC @ 500 mA.

Note: The power supply must be connected to the Model 65A, through the 1.3 mm connector located on the side of the unit, prior to plugging the power supply into the wall.
 

8.0 Help

If you require assistance, please visit our Technical Support Center.
 

Warranty

TELEBYTE warrants the equipment to be free from defects in material and workmanship, under normal and proper use and in its unmodified condition, for 12 months, starting on the date it is delivered for use. TELEBYTE's sole obligation under this warranty shall be to furnish parts and labor for the repair or replacement of products found by TELEBYTE to be defective in material or workmanship during the warranty period. Warranty repairs will be performed at the point of manufacture. Equipment approved for return for warranty service shall be returned F.O.B. TELEBYTE factory and will be redelivered by TELEBYTE freight prepaid, except for non-continental U.S.A. locations. Non-continental deliveries will be sent COD freight plus import/export charges.

The above warranty is in lieu of all other warranties, expressed or implied, statutory or otherwise, including any implied warranty of merchantability or fitness for a particular purpose. TELEBYTE shall not be liable for any damages sustained by reseller or any other party arising from or relating to any equipment failure, including, but not limited to consequential damages nor shall TELEBYTE have any liability for delays in replacement or repair of equipment.

Out of warranty equipment may be returned to the Greenlawn, NY customer service facility prepaid as described above. Return shipping charges will be billed to the customer. The repaired unit will have a 90-day warranty. In those cases where "NO TROUBLE" is found, a reduced charge will be billed to cover handling, testing and packaging.

Whether in or out of warranty, a Return Material Authorization (RMA) number is necessary and can be obtained by visiting our Technical Support Center.  Reference the RMA number on the outside container.

 
Document No. 0315-0261/Rev. B
 

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