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Some terminology will be defined to aid the user in understanding cable requirements
in Table 4-5. Reference is often made to the "RS-232C" standard, for data communi-
cation. The RS-232C standard describes mechanical, electrical, and functional char-
acteristics. This standard is published by the Electronics Industry Association (EIA)
and use of the standard is voluntary but widely accepted for electronic data transfer.
ABB relay communications follows the RS-232C standard for non-network data com-
munication.
Although the RS-232C standard does not specify a connector shape, the most com-
monly used is the "D" shape connector. As stated in Section 4.6.2 above, all ABB relay
communication connectors are of the "D" shape (such as DB-25S).
Data communication devices are categorized as either Data Terminal Equipment (DTE)
or Data Communication Equipment (DCE). A DTE is any digital device that transmits
and/or receives data and uses communications equipment for the data transfer.
DCE's are connected to a communication line (usually a telephone line) for the pur-
pose of transferring data from one point to another. In addition to transferring the da-
ta, DCE devices are designed to establish, maintain, and terminate the connection. As
examples, a computer is a DTE device and a modem is a DCE device.
By definition the connector of a DCE is always female (usually DB-9S or 25S). Simi-
larly, DTEs are always male (usually DB-9P or 25P). These definitions apply to the
equipment being connected and to the connectors on the interconnecting cables.
One additional piece of hardware that is required, in some applications, is a "null" mo-
dem. Null modem's function is to connect the transmit line (TXD), pin 2 (of a 25 pin
connector) by RS-232C standard, to the receive line (RXD), pin 3. A null modem is re-
quired when connecting like devices. That is DTE to DTE or DCE to DCE. A DCE to
DCE, for example, where a null modem is required, is the connection of a 25 pin, PONI
to a modem.
A null modem function can be accomplished in the connecting cable or by separate
null modem connector. That is, by using a conventional RS-232C cable plus a null mo-
dem. One type of null modem, available from electronics suppliers, is B & B Electron-
ics Type 232MFNM.
4. 7.
FRONT RS-232C COMMUNICATIONS PORT
4.7.1
Communications Port Set Up
The front RS-232C comm. port on the relay, consists of a printed circuit board that
plugs flat into the rear of the microprocessor module. On the front panel, of the relay,
is the 9-pin (DB-9S) DCE connector with it's associated enabling push-button, next to
the connector. As described above, communications with the relay requires a serial ca-
ble from the comm. port to the communicating device (usually a local PC).
The front comm. port data rate must match the comm. port data rate of the device con-
nected to the port. This data rate is set when configuring communications on the com-
municating device. If the communicating device is a PC, the data rate is set by RCP
either when setting up RCP or by changing settings while running RCP.
To set the data rate on the front comm. port, the five dip switch poles of switch S1 (see
Figure 1-13) must be set according to Table 4-6. When the relay is viewed from the
front, (front cover removed) the switch S1 is located on the right side of the front panel
(10/94)
I.L. 40-386.3
4-9
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