Omega OMEGABUS A2400 Manual de usuario
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User’s Guide
A2400 Series
Radio Modem Module
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WARNING: These products are not designed for use in, and should not be used for, human applications.
A2400 USERS MANUAL
REVISED: 4/17/95
OMEGA ENGINEERING
ONE OMEGA DRIVE
P. O. BOX 4047
STAMFORD, CT 06907
PHONE: 1-800-DAS-IEEE
FAX: 203-359-7990
e-mail: [email protected]
www.omega.com
The information in this publication has been carefully checked and
isbelievedtobeaccurate;however,noresponsibilityisassumedfor
possibleinaccuraciesoromissions.Applicationsinformationinthis
manualisintendedassuggestionsforpossibleuseoftheproducts
andnot as explicit performancein a specific application.Specifica-
tions may be subject to change without notice.
The A2400 series are not intrinsically safe devices and should not
be used in an explosive environment unless enclosed in approved
explosion-proof housings
TABLE OF CONTENTS
CHAPTER 1 Getting Started
Quick Hook-Up 1-3
Default Mode 1-4
CHAPTER 2 Functional Description
Block Diagram 2-1
CHAPTER 3 Communications
RS-485 3-2
Multi-party Connection 3-3
RS-485 Multidrop System 3-4
CHAPTER 4 Command Set
Table of Commands 4-6
User Commands 4-6
Error Messages 4-13
CHAPTER 5 Setup Information and Command
Command Syntax 5-1
Setup Hints 5-8
CHAPTER 6 Delay Time Programming
CHAPTER 7 Power Supply
CHAPTER 8 Troubleshooting
CHAPTER 9 Extended Addressing
CHAPTER 10 Transparent Mode
Chapter 1
Getting Started
Introduction
This manual describes the function and application of the Radio Modem
Interface Module (A2400). The A2400 provides an intelligent interface
between radio modems available from many manufacturers and devices
designed to operate on a bi-directional RS-485 serial bus. Although the
A2400 has been designed specifically for our family of industrial I/O
modules, it may also be used with other RS-485 devices.
Figure 1.1 depicts a typical application that incorporates A2400’s. In many
data acquisition situations, the sensor data is inaccessible to the host
computer due to large distances or the lack of telephone facilities to
incorporateconventionaldial-upmodems.Insomecases,sensordatamay
have to be monitored full time and the cost of telephone service can be
prohibitive.Fortheseandamultitudeofotherreasonstheuseofaradiolink
can be the best solution.
Unfortunately,radio modemsaredesignedforcomputer-to-computercom-
munications and require a certain amount of intelligence at each radio site
in order to construct useful systems. The cost of a local computer at each
radiocaneasilymakethe concept impractical. The Radio Modem Interface
Module(A2400)fillstheneedforalow-costintelligentinterfacebetweenthe
radio modem and the RS-485 data acquisition devices.
In a typical system as shown in Figure 1.1, there is one host or master
computer and any number of slave sites. The master radio transmitter and
the slave receivers communicate on the same radio frequency, and of
course,theslavetransmittersandthemasterreceiveraretunedtothesame
frequency. While it is common to use two frequencies for simultaneous
transmitting and receiving, it is possible to use one frequency for all
communications. In an idle condition all slave transmitters are turned off.
Each slave site is assigned a unique address so that the master may direct
commands to a particular site. To initiate a communications sequence, the
masterwilltransmita commandbyradiowhichis receivedbyalltheslaves.
Thetransmittedcommandcontainsanaddresswhichdirectsthecommand
to a particular slave site. The slave site that matches the address will
respond to the command. At this time, the addressed slave site will turn on
itsradiotransmitterandcommunicatebackto themasterinresponsetothe
command. Once the response is complete the slave will turn off the
transmitter and wait for a new command. To avoid interference, only one
slave transmitter can be on at any given time. The primary function of the
Getting Started 1-2
A2400 is to control the slave transmitter to allow multiple slave sites.
Figure 1.1 System Overview.
Leased Lines
This manual has been written with emphasis on radio modems. However,
the A2400’s may be used just as effectively with leased telephone lines.
Typically, leased lines do not have dial-up capability and some means of
addressingandmultiplexingmustbeemployedifmultiplestationsareused.
A2400’s may be used with leased line modems in an identical manner as
with radio modems.
Getting Started 1-3
Getting Started
To get your A2400 up and running for an initial check-out, connect the unit
to a power supply and terminal as shown in Figure 1.2. The power supply
can be any dc source from 10 to 30 volts, capable of 1 Watt of power. The
terminal can be any RS-232 dumb terminal set for 300 baud. A computer
configuredasaterminalcanalsobeused.BesuretogroundtheDEFAULT*
pin.
Figure 1.2 A2400 Quick Hookup.
After checking the connections, power up the A2400. Type the following
command on the terminal:
$1RD
Makesuretouseuppercasecharactersforthe‘RD’(ReadData)command
andterminate the command withacarriagereturn. The A2400shouldreply
with the message:
*+99999.99
Getting Started 1-4
Thismessageisterminatedwithacarriagereturn.Iftheresponsemessage
cannot be obtained, re-check all the wiring, making sure that the proper
power is on the A2400 connector and that the DEFAULT* line is shorted to
the GND pin. The terminal must be set to 300 baud.
If, after several attempts, the response message does not appear, refer to
Chapter 8 Troubleshooting in this manual.
If you have an IBM PC or compatible computer, running the S1000 setup
software will ease the task of setting up the A2400 for your application.
AfterestablishingcommunicationswiththeA2400,readthemanualandfeel
free to experiment with the various commands and setups available. If
communicationsislostduetoanimpropersetup,returningbacktothehook-
up of Figure 1.2 will restore communications to the A2400.
Default Mode
The A2400 contains an EEPROM (Electrically Erasable Programmable
ReadOnlyMemory)tostoresetupinformation.TheEEPROMreplacesthe
usualarrayofswitches necessarytospecifybaudrate, address,parity,etc.
The memory is nonvolatile which means that the information is retained
even if power is removed. No batteries are used so it is never necessary to
open the module case.
The EEPROM provides tremendous system flexibility since all of the setup
parameters may be configured remotely through the communications port
withouthavingtophysically changeswitchsettings.Thereis oneoneminor
drawbackinusingEEPROMinsteadofswitches;thereisnovisualindication
of the setup information in the module. It is impossible to tell just by looking
at the A2400 what the baud rate, address, parity and other settings are. It
is difficult to establish communications with a A2400 whose address and
baud rate are unknown. To overcome this, the A2400 has a pin labeled
DEFAULT*. By connecting this pin to ground (GND) the A2400 is forced to
a known communications setup called Default Mode.
TheDefaultMode setup is: 300 baud, no parity, any addressisrecognized.
Grounding the DEFAULT* pin does not change any of the setups stored in
EEPROM.ThesetupmaybereadbackwiththeReadSetup(RS)command
to determine the communications parameters stored in the A2400.
AnA2400 in Default Mode will respond toany address except the six illegal
Getting Started 1-5
values (NULL, CR, $, #, {, }). A dummy address must be included in every
command for proper responses.
Setup information in an A2400 may be changed at will with the SetUp (SU)
command. Baud rates and parity setups may be changed without affecting
the Default values of 300 baud and no parity. When the
DEFAULT* pin is released, the module automatically performs a program
reset and configures itself to the baud rate and parity stored in the setup
information.
TheDefaultModeisintended to be used with a single module connected to
a terminal or computer for the purpose of identifying and modifying setup
values. During normal operation, the DEFAULT* pin should be left open.
Chapter 2
Functional Description
Block Diagram
The A2400 is an RS-232/RS-485 converter specifically designed to inter-
face D series RS-485 modules to radio modems. To this end the A2400
provides three functions:
1) Perform the RS-232 to RS-485 electrical conversion.
2) Control the data direction of the RS-485 bus.
3) Create hand-shaking signals to control the modem.
A simplified block diagram of the A2400 is illustrated in Figure 2.1. This
shows the RS-485 and RS-232 drivers connected to their respective
interface pins. The A2400 contains two UARTs (Universal Asynchronous
Receiver / Transmitters), one dedicated to each port. The RS-485 port is
connectedtoaUARTthatisintegraltothesupervisorymicroprocessor.The
RS-232portconnectstoasecondUARTexternaltothemicroprocessor.All
datacommunicatedtoandfromtheA2400oneitherportmustpassthrough
the microprocessor. The micro controls the data flow depending on the
content of the data and setup information specified by the user.
The A2400 contains an Electrically Erasable Programmable Read-Only
Memory (EEPROM) which is used to store operating parameters specified
bytheuser.TheEEPROMwillretainthesetupdataevenifpowerisremoved
from the A2400. The EEPROM requires no battery and is guaranteed to
retain data for at least ten years. The setup data stored in the EEPROM
includes the baud rate, address, parity, timing data, etc. When power is
appliedtotheA2400,theinternalmicroprocessorreadsthesetupdatafrom
the EEPROM and automatically configures itself. The setup data may be
downloaded with a terminal or computer connected to the RS-232 port.
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