B&B 485DSS User Manual

Distributed Smart Switch

Model 485DSS

Document No. 485DSS3298

This product

Designed and Manufactured

In Ottawa, Illinois

USA

of domestic and imported parts by

B&B Electronics Mfg. Co. Inc.

707 Dayton Road -- P.O. Box 1040 -- Ottawa, IL 61350

PH [phone] -- FAX [phone]

Internet:

http://www.bb-elec.com

[e-mail]

[e-mail]

 1998 B&B Electronics -- August 1998

TABLE OF CONTENTS

CHAPTER 1: HARDWARE ...................................................................1

INTRODUCTION.........................................................................................1

Figure 1. Example of an RS-485/422 Multi-Node Network.......................1

CHECKLIST ...............................................................................................1

SPECIFICATIONS........................................................................................2

Figure 2. Top View of Circuit Board...........................................................2

PORT CONFIGURATION..............................................................................2

RS-485/422 Port..................................................................................2

Table 1. RS-422/485 Port ......................................................................3

RS-232 Port .........................................................................................3

Table 2. RS-232 DTE DB25P Connector Chart.....................................4

RS-422/485 Wiring ..............................................................................4

2-Wire Mode........................................................................................4

Table 3. Component Values For Send Data Timing...............................5

Figure 3. RS-485 Wiring Diagram .............................................................6

4-Wire Mode........................................................................................6

Figure 4. RS-422 Wiring Diagram .............................................................7

RS-485 AND RS-422 TERMINATION.........................................................7

POWER SUPPLY.........................................................................................7

OPERATION...............................................................................................8

Figure 5. Simplified Functional Diagram...................................................9

COMMUNICATION CONFIGURATION ..........................................................9

DISTRIBUTED SMART SWITCH COMMANDS...............................................9

The Command String.........................................................................10

ON Command ....................................................................................10

OFF Command..................................................................................11

STATUS REQUEST Command..........................................................11

SETTING THE 485DSS ADDRESS.............................................................14

Table 4. Address Switch.......................................................................14

BINARY FILE TRANSFER .........................................................................15

CHAPTER 2: SOFTWARE...................................................................16

DESCRIPTION.........................................................................................16

HARD DRIVE INSTALLATION...................................................................16

RUNNING DEMONSTRATION PROGRAM.................................................17

APPENDIX A: ASCII CHARACTER CODES .................................A-1

APPENDIX B: DECIMAL/HEXADECIMAL CONVERSIONS......B-1

Table 5. Hex/Dec Conversions................................................................B-1

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APPENDIX C: CABLE CHARTS ......................................................C-1

CHART 1. IBM PC DB25 CONNECTOR TO ..........................................C-1

485DSS RS-232 (DTE) PORT ...........................................................C-1

CHART 3. RS-232 DCE DEVICE W/DB25 CONNECTOR TO..................C-1

485DSS RS-232 (DTE) PORT ...........................................................C-1

CHART 2. IBM PC DB9 CONNECTOR TO ............................................C-1

485DSS RS-232 (DTE) PORT ...........................................................C-1

CHART 4. RS-232 DCE DEVICE W/DB9 CONNECTOR TO....................C-2

485DSS RS-232 (DTE) PORT ...........................................................C-2

CHART 5. RS-422/485 4-WIRE DEVICE TO 485DSS RS-422/485PORT C-2

CHART 6. RS-485 2-WIRE DEVICE TO 485DSS RS-485/422 PORT.....C-2

ii Table of Contents 485DSS3298 Manual

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Chapter 1: HARDWARE
Introduction

The RS-485 Distributed Smart Switch (485DSS) connects one

RS-232 device to an RS-485 multi-node network as shown in Figure

1. To accomplish this, the 485DSS converts RS-232 to an
addressable RS-485 node. A unique address, from 0 to 255, is user
assigned by setting switches on the 485DSS.

Figure 1. Example of an RS-485/422 Multi-Node Network

Checklist

The following items should be in the shipping carton:

1. RS-485 Distributed Smart Switch

2. Instruction Manual

3. (1) 3 1/2" floppy disk
Contact the shippers immediately if any of the items above is

missing or has damage.

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Specifications

Model: 485DSS
Size: 4.8"L x 2.15"W x 0.9"H
Power: +11 to 16 Vdc 75mA
RS-232 Connection: DB-25 male (DTE configured)
RS-485 Connection: Terminal Blocks
Communications: 9600 baud, no parity, 8 data bits, 1 stop bit

Figure 2. Top View of Circuit Board

Port Configuration

The 485DSS has a RS-485/422 port and a RS-232 port. The
RS-485/422 signals are on terminal blocks. Table 1 shows you the
pinouts and Figure 2 shows you the location of the terminal blocks.
The RS-232 signal, in the DTE configuration, connects to a DB25
male connector. Table 2 shows you the RS-232 pinouts.

RS-485/422 Port

The RS-485 port on the 485DSS receives and transmits data to
and from the RS-485 network. The RS-485 port has a balanced
differential line driver and receiver. RS-485 allows up to 32 driver
and receiver pairs to share a two-wire party line network. This port
will operate on a 4-wire network and is compatible with RS-422
devices. Refer to B&B Electronics’ free RS-422/485 Application Note
for more information. Refer to Appendix C for cable charts.

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Table 1. RS-422/485 Port

Terminal
Block
Signal Description

RS-422/485
Signal
Direction of
Port

FR GND Frame Ground <------>

TD(A)(-) Transmit Data (A)(-) Output

TD(B)(+) Transmit Data (B)(+) Output

RD(A)(-) Receive Data (A)(-) Input

RD(B)(+) Receive Data (B)(+) Input

GND Signal Ground <------>

+12VDC Power Supply Input

RS-232 Port
The RS-232 DTE port is an asynchronous port that supports TD

and RD signals. In order to make the proper connections to the RS­232 port. It is necessary to have a basic understanding of the terms
DCE and DTE. The original design for connecting RS-232 devices
together uses DB25 connectors, and connects a DTE (Data

Terminal Equipment) device to a DCE (Data Communication
Equipment) device. Each device will have inputs on pins that

correspond to outputs on the same pins of the other device. For
example, a DTE device transmits data out on pin 2 and a DCE
device receives data in on pin 2. IBM PC's are DTE devices and
modems are DCE devices. Only TD and RD of the RS-232 port
pass through to the RS-485 port when the 485DSS is ON. The
485DSS raises and lowers the RTS output signal on the RS-232 port
to reflect the connect state of the port. This signal can notify the RS­232 device to start communicating to the Host or it can be an alarm
output. The Host can monitor the CTS input line to determine if the
RS-232 device is requesting access to the network. This input line
could also be an alarm input. NOTE: If using RTS or CTS lines as
alarms the user may have to design additional circuitry to properly
interface to the alarm circuits. Refer to cable charts in Appendix C
for making your own cables.

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Table 2. RS-232 DTE DB25P Connector Chart

Signal
Direction of
RS-232 DTE

Pin # Signal Description

FR GND Frame Ground <------>

1

TD Transmit Data Output

2

RD Receive Data Input

3

RTS Request to Send Output

4

CTS Clear to Send Input

5

SG Signal Ground <------>

7

Port

RS-422/485 Wiring

RS-485 receivers also have an enable/disable control line. The
2W/4W jumper selects when to enable and disable RS-485 receiver.
Setting the jumper to the 4W position constantly enables the
receiver which is the same as operating in an RS-422/485 4-wire
mode. In this position and connected to a 2-wire network, all data
being transmitted by the RS-485 driver echos back through the RS­485 receiver. Setting the jumper to 2W (RS-485, 2-wire mode)
automatically enables the receiver when the RS-485 driver disables
and visa versa.

To configure the 485DSS for a typical 2-wire party line network,
set the jumper in the 2W position. Refer to Figure 2 for the jumper
location.

The EIA RS-485 Specification labels data lines with an "A" and
"B" designator. Some RS-485 equipment uses a "+" and "-"
designator. In almost all cases, the "A" line is the equivalent of the "­" line and the "B" line is the equivalent of the "+" line. See Figure 3
for a wiring example.

2-Wire Mode

RS-485 allows half-duplex communications of multiple drivers
having a control line for enabling and disabling (tri-stating) their
outputs. When the 485DSS transmits a status reply message to the
Host, the microcontroller will automatically enable the driver before
transmitting the first character of the reply and disable the driver
after the last character of the reply. When the 485DSS is ON
(selected) and the RS-232 device is transmitting data to the Host the
Send Data (SD) control circuit enables and disables the driver. The
485DSS disables the driver when it is not transmitting data to the
Host and listens to (receives) all communications on the network.

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SD control automatically enables the RS-485 driver by sensing
the leading edge of the first character transmitted to the RS-232
port. After transmitting the last character, the send data timer circuit
waits one character time (1 millisecond at 9600 baud) before
disabling the RS-485 driver.

There are two components in the timer circuit, a resistor (R15)
and a capacitor (C10), that make up the send data control circuit.
These components are factory selected for 9600 baud, allowing the
send data control to operate at 9600 baud or higher. These two
components disable the RS-485 driver approximately 1 millisecond
after transmitting the last character. To change to a baud rate lower
than 9600 baud, or to configure the send data control to match a
specific baud rate of the RS-232 device, remove R15 and insert the
value specified in Table 3 into the R21 position. Use Figure 2 to
locate R15 and C10. NOTE: The SD timing circuit does not control
the RS-485 driver when the 485DSS sends reply messages to the
host.

Table 3. Component Values For Send Data Timing

Baud Rate Time (ms)

Resistor Value

R15 (ohms)

Capacitor Value

C10(microfarads)

1200 8.33 820K .01
2400 4.16 430K .01
4800 2.08 200K .01

9600* 1.04* 100K* .01*
19200 0.520 56K .01
38400 0.260 27K .01
56700 0.176 16K .01

115200 0.0868 8.2K .01

* Factory Default

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