Manual

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ACB-MP.PCI User Manual

RS-485

RS-485 is backwardly compatible with RS-422; however, it is optimized for

partyline or multi-drop applications. The output of the RS-422/485 driver is capable

of being Active (enabled) or Tri-State (disabled). This capability allows multiple

ports to be connected in a multi-drop bus and selectively polled. RS-485 allows

cable lengths up to 4000 feet and data rates up to 10 Megabits per second. The signal

levels for RS-485 are the same as those defined by RS-422. RS-485 has electrical

characteristics that allow for 32 drivers and 32 receivers to be connected to one line.

This interface is ideal for multi-drop or network environments. RS-485 tri-state

driver (not dual-state) will allow the electrical presence of the driver to be removed

from the line. Only one driver may be active at a time and the other driver(s) must

be tri-stated. RS-485 can be cabled in two ways, two wire and four wire mode. Two

wire mode does not allow for full duplex communication, and requires that data be

transferred in only one direction at a time. For half-duplex operation, the two

transmit pins should be connected to the two receive pins (Tx+ to Rx+ and Tx- to

Rx-). Four wire mode allows full duplex data transfers. RS-485 does not define a

connector pin-out or a set of modem control signals. RS-485 does not define a

physical connector.

RS-530 / 530A

RS-530 (a.k.a. EIA-530) compatibility means that RS-422 signal levels are met, and

the pin-out for the DB-25 connector is specified. The EIA (Electronic Industry

Association) created the RS-530 specification to detail the pin-out, and define a full

set of modem control signals that can be used for regulating flow control and line

status. The major difference between RS-530 and RS-530A lies in some of the

modem control interface signals. In RS-530 the signals all of the modem control

signals are differential, in RS-530A some of these signals are single ended. The

RS-530 specification defines two types of interface circuits, Data Terminal

Equipment (DTE) and Data Circuit-Terminating Equipment (DCE). The Sealevel

Systems adapter is a DTE interface.

V.35

V.35 is a standard defined by ITU (formerly CCITT) that specifies an electrical,

mechanical, and physical interface that is used extensively by high-speed digital

carriers such as AT&T Dataphone Digital Service (DDS). ITU V.35 is an

international standard that is often refereed to as Data Transmission at 48 Kbps

Using 60 - 108 KHz Group-Band Circuits. ITU V.35 electrical characteristics are a

combination of unbalanced voltage and balanced current mode signals. Data and

clock signals are balanced current mode circuits. These circuits typically have

voltage levels from 0.5 Volts to -0.5 Volts (1 Volt differential). The modem control

signals are unbalanced signals and are compatible with RS-232. The physical

connector is a 34 pin connector that supports 24 data, clock and control signals. The

physical connector is defined in the ISO-2593 standard. ITU V.35 specification

defines two type of interface circuits, Data Terminal Equipment (DTE) and Data

Circuit-Terminating Equipment (DCE). The Sealevel Systems adapter is a DTE

interface.