RS530 interface

a Tutorial

AC & PIN powered - Converter, Opto Isolation, Drivers, Fiber Modems



RS530 is just like RS422 and uses a differential signaling on a DB25 - RS232 format - EIA-530 Transmit (and the other signals) use a twisted pair of wires (TD+ & TD-) instead of TD and a ground reference as in RS232 or V.24. This interface is used for HIGH SPEED synchronous protocols. Using a differential signaling allows for higher speeds over long cabling.

1.4 Signaling Rates

This standard is applicable for use at data signaling rates in the range from 20,000 to a nominal upper limit of 2,000,000 bits per second. Equipment complying with this standard, however, need not operate over this entire data signaling rate range. They may be designed to operate over a narrower range as appropriate for the specific application.


(1) EIA-422-A 1; "Electrical Characteristics of Balanced Voltage Digital Interface Circuits"

The individual Category I circuits shall use the balanced electrical characteristics of EIA-422-A. Two leads shall be brought out to the interface connector for each Category I circuit as shown in Figure 2.1(a). Thus, each interchange circuit consists of a pair of wires interconnecting a balanced generator and a differential receiver.

The point of demarcation between the DTE and the DCE is located at a plugable connector signal interface point between the two equipments which is less than 3 meters (10 feet) from the DCE. A 25-position connector is specified for all interchange circuits.

The DCE shall be provided with the connector having female contacts and a male shell. The connector shall be either physically attached to the DCE or extended by means of a short cable (lees than 3 meters or 10 feet). The DTE shall be provided with a cable having the connector as specified having male contacts and a female shell. The total length of the cable associated with the DTE shall not exceed 60 meters (200 feet) for non-tailored applications or up to 1 kilometer on a tailored network. The mechanical configuration for connections of the interface cable at points other than the point of demarcation is not specified.

The relationship between signaling rate and interface cable distance for balanced interchange circuits is specified in EIA-422-A. Using the guidelines of EIA-422-A, operation over 60 meters (200 feet) of cable limits the maximum signaling rate of balanced interchange circuits to 2,000,000 bits per second. Timing signals, which operate at twice the signaling rate of data signals, may be up to 4,000,000 bits per second. Operation over cable distances greater than 60 meters (200 feet) can be accomplished, in many cases, but is limited to 1 kilometer and is considered a tailored application.


RS232 to RS530 converter pin out
using an active unit in the middle 

FOR  RS-530

When choosing a transmission line, it is necessary to examine the required distance of the cable and the data rate of the system.  Losses in a transmission line are a combination of ac losses (skin effect), dc conductor loss, leakage, and ac losses in the dielectric. In high quality cable, the conductor losses and the dielectric losses are on the same order of magnitude.


Selecting data cable for a system isn't difficult, but often gets lost in the shuffle of larger system issues. Care should be taken, however, because intermittent problems caused by marginal cable can be very difficult to troubleshoot.

Beyond the obvious traits such as number of conductors and wire gauge, cable specifications include a handful of less intuitive terms.

Characteristic Impedance (Ohms): A value based on the inherent conductance, resistance, capacitance and inductance of a cable that represents the impedance of an infinitely long cable. When the cable is cut to any length and terminated with this Characteristic Impedance, measurements of the cable will be identical to values obtained from the infinite length cable. That is to say that the termination of the cable with this impedance gives the cable the appearance of being infinite length, allowing no reflections of the transmitted signal. If termination is required in a system, the termination impedance value should match the Characteristic Impedance of the cable.

Shunt Capacitance (pFft): The amount of equivalent capacitive load of the cable, typically listed in a per foot basis. One of the factors limiting total cable length is the capacitive load. Systems with long lengths benefit from using low capacitance cable.

Propagation velocity (% of c): The speed at which an electrical signal travels in the cable. The value given typically must be multiplied by the speed of light (c) to obtain units of meters per second. For example, a cable that lists a propagation velocity of 78% gives a velocity of 0.78 X 300 X 10' - 234 X 106 meters per second.

Plenum cable

Plenum rated cable is fire resistant and less toxic when burning than non-plenum rated cable. Check building and fire codes for requirements. Plenum cable is generally more expensive due to the sheathing material used.

The RS-422 specification recommends 24AWG twisted pair cable with a shunt capacitance of 16 pF per foot and 100 ohm characteristic impedance. While the RS-530 specification does not specify cabling, these recommendations should be used for RS-530 systems as well.

It can be difficult to quantify whether shielding is required in a particular system or not, until problems arise. We recommend erring on the safe side and using shielded cable. Shielded cable is only slightly more expensive than unshielded.

There are many cables available meeting the recommendations of RS-422 and RS-485, made specifically for that application. Another choice is the same cable commonly used in the twisted pair Ethernet cabling. This cable, commonly referred to as Category 5 cable, is defined by the EIA/TIA/ANSI 568 specification. The extremely high volume of Category 5 cable used makes it widely available and very inexpensive, often less than half the price of specialty RS530 cabling. The cable has a maximum capacitance of 17 pF/ft (14.5 pF typical) and characteristic impedance of 100 ohms.

Category 5 cable is available as shielded twisted pair (STP) as well as unshielded twisted pair (UTP) and generally exceeds the recommendations for RS-422 making it an excellent choice for RS-530 systems.

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