B&B Electronics 485DSS User manual

485DSS-0308 Manual Cover Page
B&B Electronics Mfg Co Inc – 707 Dayton Rd - PO Box 1040 -Ottawa IL 61350 - Ph 815-433-5100 - Fax [phone]
B&B Electronics – Westlink Commercial Park – Oranmore, Galway, Ireland – Ph [phone] – Fax [phone]
Distributed Smart Switch
Model 485DSS
Documentation Number 485DSS-0308
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
[email protected]
[email protected]
©1998 B&B Electronics -- January 2008

485DSS-0308 Manual Table of Contents i
B&B Electronics Mfg Co Inc – 707 Dayton Rd - PO Box 1040 -Ottawa IL 61350 - Ph 815-433-5100 - Fax [phone]
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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
APPENDIX A: ASCII CHARACTER CODES ................................A-1
APPENDIX B: DECIMAL/HEXADECIMAL CONVERSIONS.....B-1
Table 5. Hex/Dec Conversions ............................................................... B-1
APPENDIX C: CABLE CHARTS......................................................C-1

ii Table of Contents 485DSS-0308 Manual
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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-422/485 PORTC-2
CHART 6. RS-485 2-WIRE DEVICE TO 485DSS RS-485/422 PORT. ....C-2

485DSS-0308 Manual 1
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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.
Checklist
The following items should be in the shipping carton:
1. RS-485 Distributed Smart Switch
2. Instruction Manual
3. Software
Contact the shippers immediately if any of the items above is
missing or has damage.
Figure 1. Example of an RS-485/422 Multi-Node Network

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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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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 RS-
232 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
RS-232 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.
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

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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 RS-
485 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.
Table 2. RS-232 DTE DB25P Connector Chart
Pin #
Signal
Description
Signal
Direction of
RS-232 DTE
Port
1 FR GND Frame Ground <------>
2 TD Transmit Data Output
3 RD Receive Data Input
4 RTS Request to Send Output
5 CTS Clear to Send Input
7 SG Signal Ground <------>

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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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Figure 3. RS-485 Wiring Diagram
4-Wire Mode
To configure the 485DSS for RS-485 or 422 four-wire mode,
place the jumper in the 4W position. Refer to Figure 4 for
connecting information and Figure 2 for the jumper location. In this
position on a 4-wire network the Host and the RS-232 device can
communicate in full duplex. CAUTION: Data loss may occur if the
Host sends 485DSS commands while the host is receiving data from
the network!

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Figure 4. RS-422 Wiring Diagram
RS-485 and RS-422 Termination
A jumper labeled “TERM” provides termination for the RS-
485/422 receiver. The termination resistor is a 120-ohm resistor
placed between the RD (A) and RD (B) lines. To use this
termination, place the jumper in the "IN" position. Refer to Figure 2
for the location of this jumper. If there is no need for termination,
place the jumper in the "OUT" position. For more discussion of
termination refer to B&B Electronics’ free RS-422/485 Application
Note.
Power Supply
The 485DSS requires an unregulated DC power source that will
supply +12 volts at 100 milliamps. Connect the positive side of the
power source to the +12VDC terminal block and the common side of
the power source to the GND terminal block. Refer to Figure 2 for
the location of the terminal blocks and the polarity. B&B Electronics'
power supply Model 485PS2 is available for the 485DSS.

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Operation
The host computer of the RS-485 network controls each
485DSS on the network by sending them command messages.
These commands can turn a 485DSS on or off, and can also
request status from an individual or from all of the 485DSS's on the
network. The communication setup used to send and receive these
commands are: 9600 baud, 8 data bits, no parity, and 1 stop bit.
Each command consists of four characters: a start of message
character, two address characters, and the command character. All
485DSS's on the network will receive the command message strings
sent by the Host, but only the 485DSS with the matching address
will execute the command. Execution of the ON command raises
the Request To Send (RTS) output line on pin 4 of the DB25
connector and connects the RS-232 port to the RS-485 network.
Once ON (selected), the RS-232 device can transmit and receive
data to the HOST. Executing the OFF command lowers the RTS
line, disconnecting the RS-232 port from the network. The RS-232
port of the 485DSS is OFF (not selected) at power up. The 485DSS
does not buffer or delay any data passing through the unit. ALL data
that is sent from the RS-485 device will be passed through to the
RS-232 side while the unit is selected including the next set of
command characters.
The Host can poll any or all 485DSS's on the network using the
request status command. This allows the Host to determine if any
485DSS is requesting access to the network by monitoring the
handshake status character returned by the 485DSS. The status
character reflects the state of the input handshake signal Clear To
Send (CTS) on the RS-232 connector pin 5. With this feature the
Host has the ability to prioritize each 485DSS on the network. Refer
to Figure 2.

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Three red LED indicators are located on top of the 485DSS.
The LED labeled TD flashes when the RS-232 device is transmitting
data. The LED labeled RD flashes when data is being received by
the 485DSS from the RS-485 network. The LED labeled SEL turns
on indicating that the RS-232 device has access to the RS-485
network. Refer to Figure 2. Terminal blocks on the 485DSS
connect the RS-485 signals, and input power to the unit. The RS-
232 DTE signals of the 485DSS connect to a DB25 male connector.
An eight-position switch located in the top center of the 485DSS sets
the 485DSS's unique address.
Communication Configuration
Before the HOST can communicate with a 485DSS, the
HOST must set its communication format to: 9600 baud, 8 data bits,
no parity, and 1 stop bit. After communicating with the 485DSS, the
HOST can reset its communication format to match the format of the
RS-232 device attached to the 485DSS. ALL data is passed through
the unit after it has been selected. The 485DSS does not have any
buffering.
Distributed Smart Switch Commands
The 485DSS constantly monitors the serial data received on the
RS-485/422 port for a command string. There are only three
commands required to control the 485DSS: the ON command, the
OFF command, and the status request command.
Figure 5. Simplified Functional Diagram

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The Command String
All Command Strings consist of four ASCII characters. The first
character is the start of message character, "X-off" (decimal 19).
The second and third characters represent the hexadecimal address
of an individual 485DSS. The address range is from 0 to 255 (HEX
"00" to "FF"). Some commands require the use of the broadcast
character "DC2" (decimal 18) as the second and third characters in
the command. The fourth character is the command character.
ON Command
This command turns on an individual 485DSS and asserts the
RTS output handshake line on pin 4 of the DB25 connector. This
command allows the RS-232 device connected to the 485DSS to
access the RS-485 network. The address field in the command
string specifies which 485DSS is to turn on. All other 485DSS's on
the network will turn off if the address field does not match their
address setting.
Command character: SOH (decimal 1)
Example 1: To turn on the 485DSS set to address 15 decimal (0F
hex).
HOST transmits: Xoff “0” “F” SOH
( 19 48 70 1 decimal)
( 13 30 46 1 hex)
Example 2: To turn on the 485DSS set to address 33 decimal (21
hex).
HOST transmits: Xoff “2” “1” SOH
( 19 50 49 1 decimal)
( 13 32 31 1 hex)
Command Syntax: X-off ____ ____ ____
| | | |
| | | Command character.
| | Least signf. address character.
| Most signf. address character.
Start of message character.

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If you were writing a program in BASIC to turn on address 10
decimal (0A hexadecimal) you might form a string like this:
DSS0AON$ = CHR$(19) + "0" + "A" + CHR$(1)
You could then send DSS0AON$ to select 485DSS address 10 (0A
hex). Use similar strings for turning on the other 485DSS's.
OFF Command
This command turns off all 485DSS's on the network and lowers
the RTS output handshake line on pin 4 of the DB25 connector. The
command string consists of all non-printable ASCII characters. This
command uses two broadcast characters "DC2" (decimal 18) in the
address field. Sending this command before sending a command
that has a specific address (address characters are printable) keeps
the RS-232 device from outputting any printable characters.
NOTE: This command permits only the use of the broadcast
characters in the address field.
Command character: EOT (decimal 4)
Example 1: Turn off all the 485DSS's on the network.
HOST transmits: Xoff DC2 DC2 EOT
( 19 18 18 4 decimal)
( 13 12 12 4 hex)
The turn off string in BASIC might look like this:
DSSOFF$ = CHR$(19) + CHR$(18) + CHR$(18) + CHR$(4)
You could then send DSSOFF$ to turn off all 485DSS's.
ALL data and control characters are passed through the 485DSS
after it has been selected.
STATUS REQUEST Command
The Status Request command requests the status of an
individual 485DSS or the status of all 485DSS's on the network.
This command enables the Host computer to determine from each
reply message received if the RS-232 device is requesting access to
the network and if it has access to the network. By using this
command the Host has the ability to prioritize all the 485DSS's on
the network. A specific address in the address field specifies a

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response from an individual 485DSS. Placing broadcast characters
in the address field specifies all 485DSS's on the network. This
command temporarily turns off (disconnect) the RS-232 port from
the network while transmitting the reply message.
The reply message transmitted by the 485DSS consists of six
ASCII characters. The first character is the acknowledge character,
an upper case "A" (decimal 65). The second and third characters
represent the hexadecimal address of the 485DSS that sent the
message. The address range is from 0 to 255 (HEX "00" to "FF").
The fourth character indicates the select state of 485DSS, a "0"
(decimal 48) indicates the RS-232 port does not have a connection
(not selected) to the network and a "1" (decimal 49) indicates the
RS-232 port has a connection (selected) to the network. The fifth
character indicates the state of the CTS handshake input line on pin
5 of the RS-232 port connector. A "0" (decimal 48) indicates a low
state on the CTS input pin, and a "1" (decimal 49) indicates a high
state on the CTS input pin. The sixth character is the end of
message character, a carriage return (decimal 13).
When this command contains a specific address, the 485DSS
whose address matches the command address will wait for twenty
milliseconds before transmitting the reply message. If the command
uses the broadcast characters to receive status from all 485DSS's
on the network each 485DSS will delay transmitting its reply based
on its address. The amount of delay is equal to the unit's address in
decimal multiplied by twenty milliseconds then add an additional 20
milliseconds.
Reply Syntax: A ___ ___ ___ ___ cr
| | | | | |
| | | | | End of message char.
| | | | Handshake input state.
| | | Select State.
| | Least signf. address character.
| Most signf. address character.
Start of message character.

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Example: A unit with a decimal address of ten will have a delay of
220 milliseconds [(10 x 0.02) + 0.02 = 0.22 seconds].
Command character: ACK (decimal 6)
Example 1: To request status from the 485DSS set to address 11 (
0B hex) decimal.
HOST transmits: Xoff “0” “B” ACK
( 19 48 66 6 decimal)
( 13 30 42 6 hex)
Reply: “A” “0” “B” “0” “1” cr
The reply indicates that the RS-232 port has no connection to the
network on unit 11 and the CTS handshake line is in the high state.
Example 2: Request status from all the 485DSS's on the network.
HOST transmits: Xoff DC2 DC2 ACK
( 19 18 18 6 decimal)
( 13 12 12 6 hex)
Reply: “A” “0” “1” “0” “0” cr
Reply: “A” “0” “2” “1” “0” cr
Reply: “A” “0” “3” “0” “0” cr
Reply: “A” “1” “1” “0” “1” cr
The reply indicates the following:
Unit 1 waited 40 milliseconds and then sent a reply indicating
no connection of the RS-232 port to the network and the CTS
handshake line is in the low state.
Unit 2 waited 60 milliseconds and then sent a reply indicating
connection of the RS-232 port to the network and the CTS
handshake line is in the low state.
Unit 3 waited 80 milliseconds and then sent a reply indicating
no connection of the RS-232 port to the network and the CTS
handshake line is in the low state.

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Unit 17 decimal (11 hex) waited 360 milliseconds and then
sent a reply indicating no connection of the RS-232 port to the
network and the CTS handshake line is in the high state.
If you were writing a program in BASIC to request status from
address 5 decimal, you might form a string like this:
DSS05RS$ = CHR$(19) + "0" + "5" + CHR$(6)
You could then send DSS05RS$ to request status from 485DSS
address 5. Use similar strings for requesting status from other
individual 485DSS's.
If you were writing a program in BASIC to request status from all
the 485DSS's on the network, you might form a string like this:
DSSALLRS$ = CHR$(19) + CHR$(18) + CHR$(18) + CHR$(6)
You could then send DSSALLRS$ to request status from all the
485DSS's on the network.
Setting the 485DSS Address
Assign each 485DSS on the RS-485 network its own unique
address. To set the address use the eight position DIP switch on
the 485DSS labeled “SW1”. Refer to Figure 2 for the location of the
switch. To access this switch, you will need to remove the top cover
of the 485DSS. Insert a small screwdriver in the slot in the side of
the cover and twist to remove it. Each switch position is equal to a
specific weight value. Set the 485DSS to any decimal address from
0 to 255. To assign the new address to the 485DSS, cycle the
power on the unit.
Table 4. Address Switch
DIP Switch 1 DECIMAL WEIGHT HEX WEIGHT
1 1 1
2 2 2
3 4 4
4 8 8
5 16 10
6 32 20
7 64 40
8 128 80
OFF = Weight False ON = Weight True
Factory Default Address = 0

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Example 1: To set the address to decimal 21 (15 hex), you
would turn on switches 1, 3, and 5 (1 + 4 + 16 =
21).
Example 2: To set the address to 123 decimal (7B hex), turn on
switches 1, 2, 4, 5, 6, and 7 (1 + 2 + 8 + 16 + 32 +
64 = 123).
NOTE: It is important that the address you select is not already
being used on the network!
Binary File Transfer
When transmitting binary files through the Distributed Smart
Switch, it is possible that a string of characters could resemble a
485DSS command message. If this would happen, there could be a
disruption in the transfer process and a loss of data. A simple
solution to this problem is to change to a different baud rate before
transferring binary files.

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Chapter 2: SOFTWARE
Description
The Distributed Smart Switch Demonstration (DSS_DEMO)
Program (IBM PC or Compatible) provides the user with examples of
how to receive and transmit commands to the 485DSS. The
DSS_DEMO.EXE is a DOS executable program written in
QuickBasic that will send turn on, turn off, and status request
commands to the 485DSS. The program also monitors reply
messages from any or all 256 addresses. The source code is
written in QuickBasic (DSS_DEMO.BAS), Borland Pascal
(DSS_DEMO.PAS) and Borland and Microsoft C/C++
(DSS_DEMO.C). The source code provides an illustration of how to
send and receive commands for the 485DSS. SimpCom Version
1.03+ is required to recompile DSS_DEMO.C and
DSS_DEMO.PAS.
NOTE: This is a demonstration program only and not intended for
system applications.