B&B Electronics RS-485 User Manual 2

RS-485 Data Acquisition Module

Model 485SDA10

Document No. 485SDA103798

This product

Designed and Manufactured

In Ottawa, Illinois

USA

of domestic and imported parts by

B&B Electronics Mfg. Co. Inc.

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

PH [phone] -- FAX [phone]

Internet:

http://www.bb-elec.com

[e-mail]

[e-mail]

 1995 B&B Electronics -- Revised September 1998

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Table of Contents

Chapter 1- Introduction ...........................................1

485SDA10 Features......................................................1

Packing List...................................................................2

Software Installation......................................................2

DOS...................................................................................... 2

Windows 3.11....................................................................... 3

Windows 9x and Windows NT.............................................. 3

Uninstall.........................................................................3

Windows 3.11....................................................................... 3

Windows 9x & Windows NT................................................. 3

Getting Started..............................................................3

485SDA10 Specifications..............................................5

Analog to Digital Converter................................................... 5

5 Volt Reference................................................................... 5

Digital Inputs......................................................................... 5

Digital Outputs...................................................................... 5

Power Supply........................................................................5

Communications...................................................................5

Factory Default Settings .......................................................5

Chapter 2 - Connections..........................................6

A/D Connections............................................................6

A/D Inputs #0-10...................................................................6

A/D Ref Input +..................................................................... 6

A/D Ref Input -...................................................................... 7

Analog Ground...................................................................... 7

Typical Connections .............................................................7

Digital I/O Connections..................................................8

Digital Inputs #0-2.................................................................8

Digital Outputs #0-2.............................................................. 8

Digital Ground.......................................................................9

Typical Connections .............................................................9

Serial Port Connections............................................... 10

Power Supply Connections..........................................11

Chapter 3 - Commands..........................................12

Syntax .........................................................................13

Reading A/D Channels Command...............................13

Reading Digital I/O Command.....................................15

Set Digital Output Command....................................... 16

Set Module Address Command................................... 16

Set Power-up States Command ..................................17

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Set Turn-around Delay Command............................... 17

Read Module Configuration Command........................17

Chapter 4 - A/D .......................................................19

Sampling Rate.............................................................19

A/D Input Range..........................................................19

Reference Inputs.........................................................19

Data Range.................................................................20

Converting Data...........................................................20

Chapter 5 - Software..............................................22

Read A/D Command ...................................................22

Read Digital I/O Command..........................................23

Set Digital Output States ............................................. 24

Set Module Address ....................................................25

Set Power-up States Command ..................................26

Set Turn-around Delay ................................................27

Read Module Configuration.........................................28

Appendix A: Adding Data Field Confirmation.... A-1

Appendix B: Analog Input Impedance................B-1

Appendix C: Decimal to HEX to ASCII Table ....C-1

Figures

FIGURE 1.1 - 485SDA10 UNIT...................................................................... 1

FIGURE 1.2 - GENERAL BLOCK DIAGRAM............................................... 2

FIGURE 1.3 - A/D WITH VARIABLE RESISTOR......................................... 4

FIGURE 2.1 - TYPICAL 0-5V A/D CONNECTION ....................................... 7

FIGURE 2.2 - TYPICAL DIGITAL I/O CONNECTIONS............................... 9

FIGURE 4.1 - A/D CONVERTER DATA RANGE........................................ 20

FIGURE B-1 - EQUIVALENT INPUT CIRCUIT INCL/DRIVING SOURCEB-3

Tables

TABLE 2.1 - 485SDA10 I/O PORT PINOUT...................................... 8

TABLE 2.2 - RS-485 TERMINAL BLOCK CONNECTIONS..........10

TABLE 3.1 - 485SDA10 COMMANDS............................................. 12

TABLE 3.2 - EQUIVALENT VALUES.............................................13

TABLE 3.3 - READ A/D RESPONSE................................................ 14

TABLE 3.4 - READ DIGITAL I/O RESPONSE FOR OUTPUTS..... 15

TABLE 3.5 - READ DIGITAL I/O RESPONSE FOR INPUTS......... 15

TABLE 3.6 - SET DIGITAL OUTPUT DATA BYTE VALUES......16

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TABLE 5.1 - DIGITAL I/O MASK VALUES....................................24

TABLE A-1 EXTENDED COMMANDS........................................A-2

TABLE C-1: DECIMAL TO HEX TO ASCII TABLE.................... C-1

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Chapter 1- Introduction

485SDA10 Features

The 485SDA10 is a general purpose control module which
operates through an RS-485 interface. The 485SDA10 offers 11
channels of 10-bit A/D (analog to digital), 3 digital inputs and 3 digital
outputs. With these features, the module can be used to sense a
variety of external conditions and to control a variety of devices.

The 11 A/D channels allow you to measure voltages from 0 to 5
Volts. The 3 digital inputs and 3 digital outputs are CMOS/TTL
compatible. The A/D and digital I/O lines are available through a DB­25S (female) connector.

The 485SDA10 connects to the host computer’s RS-485 or
RS-422 serial port using terminal blocks. The address and turn­around delays are software programmable to allow use of multiple
devices or connection to existing systems. The unit automatically
detects baud rates from 1200 to 9600. A data format of 8 data bits,
1 stop bit and no parity is used.

Configuration parameters are stored in non-volatile memory.
The configuration parameters consist of the module address,
communication turn-around delay, and digital output power-up
states.

Figure 1.1 - 485SDA10 Unit

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Figure 1.2 - General Block Diagram

Packing List

Examine the shipping carton and contents for physical damage.

The following items should be in the shipping carton:

• 485SDA10 unit

• One 485SDA10 3.5” disk

• This instruction manual

• RS-485/422 Application Note

If any of these items are damaged or missing contact B&B
Electronics immediately.

Software Installation

The 485SDA10 comes with several useful programs such as a
data logging utility, a demonstration program, etc. The installation
for the SDA Logger is different depending on the platform you install
it to. Please use the one appropriate to your system.

DOS

1. Place the disk in drive A.

2. Type A: and press the <ENTER> key.

3. Type INSTALL and press the <ENTER> key.

4. Follow the instructions given by the program.

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Windows 3.11

1. Insert SDA Logger installation disk in your floppy drive.

2. Click the File Manager button.

3. Select the floppy drive containing the SDA Logger
installation disk.

4. Double click the Setup.exe icon when it appears.

5. Follow the installation instructions as prompted.

Windows 9x and Windows NT

1. Insert the SDA Logger installation disk in your floppy drive.

2. Click Start | Run.

3. Click the Browse button and choose the floppy drive
containing the SDA Logger installation disk.

4. Double click the Setup.exe icon when it appears.

5. Click the OK button to run the Setup.exe program.

6. Follow the installation instructions as prompted.

Uninstall

Uninstall for the SDA Logger version is different for each
Windows operating system. Below are the methods for uninstalling
the SDA Logger.

Windows 3.11

1. Open the File Manager in the Control Panel.

2. Click the drive that SDA Logger was installed to.

3. Click the SDA16 directory.

4. Double click the UNWISE.EXE.

5. Follow the Uninstall Wizard.

Windows 9x & Windows NT

1. Open Start | Settings | Control Panel.

2. Open ADD/REMOVE PROGRAMS.

3. Click SDA LOGGER.

4. Click the Add/Remove button.

5. Follow the Uninstall Wizard.

Getting Started

This section will provide a quick example using the 485SDA10
and the demonstration program. If you experience any problems,
refer to Chapter 2 for more precise information on connections. The
demo program continually reads the A/D inputs and the digital I/O.
The states of the digital outputs can be toggled using F2, F3, and
F4. The serial port is configured for 9600 baud, 8 data bits, no
parity, and 1 stop bit. The program supports standard addresses
and IRQ’s for COM1 and COM2.

• Connect a 0 to 5V DC analog device to A/D input #0, or you
can connect a variable resistor as shown in Figure 1.3. The

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variable resistor must be greater than 1k Ohms to limit the
output current to 5mA.

• Connect A/D Ref Input+ to +5V DC.

• Connect A/D Ref Input- to analog ground (See Figure 1.3).

• Connect the 485SDA10 to an RS-422 or 4-wire RS-485 serial

port.

Once your connections have been made, run the demo program.
Any change in A/D or digital lines on the 485SDA10 will
automatically be displayed on the screen.

Figure 1.3 - A/D with Variable Resistor

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485SDA10 Specifications

Analog to Digital Converter
Resolution: 10 bit

Channels: 11

Reference Range: 5.0V DC max. (4.888 mV per bit)

2.5V DC min. (2.444 mV per bit)
A/D Ref. Input - 0V DC to 2.5V DC
A/D Ref. Input + 2.5V DC to 5.0V DC
Input Voltage Range: -0.3V DC to 5.3V DC
Total Unadjusted Error: +/- 1 LSB max.

A/D input channels must be driven from a source impedance less
than 1kΩ.

5 Volt Reference
Output Voltage: 4.975 to 5.025V DC (5.0V DC typ.)

Accuracy: +/- 0.5 %
Output Current: 5mA max.

Digital Inputs
Channels: 3

Voltage Range: -30V DC to 30V DC
Low Voltage: -30V DC to 1.0V DC
High Voltage: 2.0V DC to 30V DC
Leakage Current: 1 µA max.

Digital Outputs
Channels: 3

Low Voltage: 0.6V DC @ 8.7mA
High Voltage: 4.3V DC @ -5.4mA

Power Supply
Input Voltage: 7V DC to 18V DC @ 30mA

(Doesn’t include the power
consumption of external devices.)

Communications
Standard: RS-422/485

Addresses: 256

Turn-around Delay: Software programmable from 0 to 255

character transmission times. (1 char.

trans. time @ 9600 baud = 1ms)
Baud Rate: 1200 to 9600 (automatic detection)
Format: 8 data bits, 1 stop bit, no parity

Connector: DB-25S (female)

Factory Default Settings

Address: ACSII “0” (48 decimal or 30h)
Turn-around Delay: 1
Power-up States: 0

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Chapter 2 - Connections

This chapter will cover the connections required for the

485SDA10. There are four sets of connections:

• A/D converter

• Digital I/O

• Serial port

• Power supply

Do not make any connections to the 485SDA10 until you have read
this chapter.
CAUTION: When making electrical connections it is important to
power down the devices being connected. If this is not possible,
precautions must be taken to ensure electrical specifications are not
exceeded.
NOTE: If you do not intend to use a section (A/D or I/O), it is still
important to read each one.

A/D Connections

The A/D connections are made on the I/O port, which is a DB­25S (female) connector. Table 2.1 shows the pinout of the I/O port.
The next sections explain the functions and connections for the
various analog signals.

A/D Inputs #0-10

These are the analog input channels. The analog data that is
read from the 485SDA10 is related to the voltage on these pins.
Connect your devices to the analog input channels. Voltages on
these inputs must remain between 0 and 5.0V DC. Connect unused
A/D inputs to analog ground.

A/D Ref Input +

The voltage connected to this pin determines the upper end of
the input voltage range. For proper operation, this pin must be
connected to a DC voltage between +2.5 and +5.0 Volts. The
485SDA10 provides a 5.0V +/-0.5% reference on pin 17. The 5V
reference can be used if you require a 0 to 5V DC input range. If
your application requires a better reference voltage or a different
input range, you must supply the appropriate reference to the
A/D Ref Input+ pin. This voltage must be at least 2.5V greater
than A/D Ref Input-. Bypassing the A/D Ref Input+ pin with 0.01µF
ceramic and 10µF tantalum capacitors to analog ground will
decrease noise levels.

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A/D Ref Input -

The voltage connected to this pin determines the low end of the
input voltage range. For proper operation, this pin must be
connected to a DC voltage between 0 and +2.5 Volts. Typically, this
is connected to your device’s ground and analog ground (0V).

Analog Ground

This pin should be connected to your analog device’s ground. If
ground (0V) is the low end of your input voltage range,
A/D Ref Input- should be connected to this pin. To minimize noise,
do not connect analog ground and digital ground together. Connect
unused A/D inputs to analog ground.

Typical Connections

Figure 2.1 shows the typical connections of the 485SDA10 for a
0 to 5V DC input range.

Figure 2.1 - Typical 0-5V A/D Connection

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Digital I/O Connections

The digital I/O connections are made on the I/O port, which is a
DB-25S (female) connector. Table 2.1 shows the pinout of the I/O
port. The next sections explain the functions and connections for
the various digital signals.

Table 2.1 - 485SDA10 I/O Port Pinout

DB-25S

Pin # Function

1 GND 14 Digital Output #0
2 +12V DC Output* 15 Digital Output #1
3 Digital Input #0 16 Digital Output #2
4 Digital Input #1 17 +5V DC Output
5 Digital Input #2 18 A/D Ref. Input +
6 Digital GND 19 A/D Ref. Input ­7 Analog GND 20 No connection
8 A/D Input #0 21 A/D Input #6

9 A/D Input #1 22 A/D Input #7
10 A/D Input #2 23 A/D Input #8
11 A/D Input #3 24 A/D Input #9
12 A/D Input #4 25 A/D Input #10
13 A/D Input #5

*Actual output is equal to power supply input minus 0.7V DC

DB-25S

Pin # Function

Digital Inputs #0-2

The digital input lines are CMOS/TTL compatible and can handle
voltages from -30V DC to +30V DC. If a digital input is from -30V
DC to 1.0V DC, the state will be read as a “0” (LOW). If a digital
input is from 2.0V DC to 30V DC, the state will be read as a “1”
(HIGH). Connect unused digital inputs to digital ground.

Digital Outputs #0-2

The digital output lines are CMOS/TTL compatible. A digital
output that is set to a “0” (LOW) will output a voltage from 0 to 0.6V
DC. A digital output that is set to a “1” (HIGH) will output a voltage
from 4.3V DC to 5.0V DC. Refer to Chapter 1, Specifications, for
more information. Unused digital output lines should be left open.

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Digital Ground

Connect the digital ground pin to your digital device's ground. To
minimize noise, do not connect analog ground and digital ground
together. Connect unused digital inputs to digital ground.

Typical Connections

Figure 2.2 shows the typical connections of the 485SDA10 for
the digital I/O lines.

Figure 2.2 - Typical Digital I/O Connections

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Serial Port Connections

To communicate with the 485SDA10 module, it must be
connected to an RS-422/RS-485 serial port. The 485SDA10 works
with 2-wire or 4-wire RS-485. The unit automatically detects baud
rates from 1200 to 9600. A data format of 8 data bits, 1 stop bit and
no parity is used. Connections are made using terminal blocks.
Table 2.2 shows the terminal blocks and their functions.

Table 2.2 - RS-485 Terminal Block Connections

TB

Label Signal

TD(A) Transmit Data (A) Output Connection is required. [Loop
TD(B) Transmit Data (B) Output Connection is required. [Loop
RD(A) Receive Data (A) Input Connection is required. [Loop
RD(B) Receive Data (B) Input Connection is required. [Loop

GND Ground - Connection for Signal GND

+12V +12 V DC Power Input Connection is required.

A typical 2-wire RS-485 connection is shown in Figure 2.3 and a
typical RS-422 (or RS-485) 4-wire is shown in Figure 2.4.

485SDA1
0 Function Notes

to RD(A) for 2-wire hookup]
to RD(B) for 2-wire hookup]
to RD(A) for 2-wire hookup]
to RD(B) for 2-wire hookup]
and Power Supply GND.

NOTE: The 485SDA10 labels the data lines with “A” and “B”
designators (per EIA RS-485 Specification). However, some RS­485 equipment used “+” and “-“ as designators. In most cases the
“A” line is the equivalent of the “-“ line and the “B” line is the
equivalent of the “+” line. With an RS-485/422 system there are
other factors that require consideration, such as termination and
turn-around delay. For more information refer to the RS-485/422
Application Note (included in packing).

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Figure 2.3 - Typical RS-485 2-wire Connection

Figure 2.4 - Typical RS-422 Connection

Power Supply Connections

The 485SDA10 requires 7 to 18 V DC at 30mA. Remember that
the 30mA requirement doesn’t include the power consumption of
any external devices. Therefore, any current sourced with the digital
outputs must be added to this value.

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Chapter 3 - Commands

There are only three commands required to control the
485SDA10:

• Read A/D command

• Read digital I/O command

• Set output states command

There are four commands used to configure the module:

• Set power-up states command

• Set turn-around delay command

• Set module address command

• Read module configuration command

The command string consists of four bytes. Some commands
require an additional data byte. For information on adding data field
confirmation to the data fields refer to Appendix A. See Table 3.1.

Table 3.1 - 485SDA10 Commands

Function Command Response
Read A/D Channels !{addr}RA{#} {ch#msb}{ch#lsb}

{ch(#-1)msb}...

{ch0msb}{ch0lsb}
Read Digital I/O !{addr}RD {I/O states}
Set Output States !{addr}SO{#} no response
Set Module Address !{addr}SA{new addr} no response
Set Power-up States !{addr}SS{#} no response
Set Turn-around Delay !{addr}SC{#} no response
Read Configuration !{addr}RC {addr}{powerup

states}{turn-around

delay}

NOTE: Each {...} represents one byte.

Before going into the specifics of each command, it is important
to understand that a byte has a value from 0 to 255 and can be
represented in decimal (0 to 255), hexadecimal (00 to FF), or by an
ASCII character. The commands in Table 3.1 are shown in ASCII,
for example:

ASCII

!0RD

<21><30><52><44>

Hex

Decimal

(33)(48)(82)(68)

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The decimal and hexadecimal equivalents of some ASCII characters
are shown in Table 3.2. Notice that the ASCII representation of the
character “0” does not have a value of 0. Refer to Appendix C for
more ASCII, decimal, and hexadecimal equivalents.

Table 3.2 - Equivalent Values

ASCII Decimal Hexadecimal

! 33 21h

0 48 30h

A 65 41h
D 68 44h
O 79 4Fh
R 82 52h

S 83 53h

NUL 0 0h

SOH 1 1h

STX 2 2h

ETX 3 3h
EOT 4 4h
ENQ 5 5h
ACK 6 6h

BEL 7 7h

Syntax

The command string consists of four bytes. The first byte is the
start of message byte. The start of message byte is always the “!”
character. The second byte is the address byte. This byte allows
each unit to have a unique address. The factory default address is
the ASCII “0” (zero) character. The next two bytes are the
command characters. These bytes are used to specify which
command the module will execute. The read A/D and digital I/O
commands require an additional data byte.

Command Syntax: ! _ _ _

| | | | |
| | | | Data Byte
| | | 2nd Command Byte
| | 1stCommand Byte
| Address Byte
Start of Message Byte

Reading A/D Channels Command

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The Read A/D channels command returns two bytes for each
channel read. The two bytes represent the most significant byte
(MSB) and least significant byte (LSB) of the reading. The MSB is
received first, followed by the LSB. This command requires a data
byte. The data byte is used to specify the number of the highest
channel to be read. All channels less than this channel will be read
as well. For example, if the data byte has a value of 6, then
channels 0 to 6 will be read. The highest channel is read first.
Command Syntax

!{addr}RA{#}

Where “{#}” is a byte that specifies the number of the highest
channel to be read. See Table 3.3
Response Syntax

{ch(#)MSB}{ch(#)LSB}{ch(#-1)MSB}...{ch0MSB}{ch0LSB}

The most significant byte of the channel specified is received first.
The least significant byte and the lower channels will follow in
descending order. “{chxMSB}” and “{chxLSB}” represent the most
and least significant bytes of the A/D conversion result.

Table 3.3 - Read A/D Response

# of Channels Specified Response
decimal Hex ASCII

Channels Returned
(order of response)

Bytes

Returned

0 0 NUL Channel 0 2

1 1 SOH Channels 1,0 4

2 2 STX Channels 2,1,0 6

3 3 ETX Channels 3,2,..,0 8

4 4 EOT Channels 4,3,..,0 10

5 5 ENQ Channels 5,4,..,0 12

6 6 ACK Channels 6,5,..,0 14

7 7 BEL Channels 7,6,..,0 16

8 8 BS Channels 8,7,..,0 18

9 9 HT Channels 9,8,..,0 20

10 A LF Channels 10,9,..,0 22

NOTE: There are three test channels that can be read: Ref+, Ref-,
and Ref+/2. Specify 13 (0Dh) to read Ref+, 12 (0Ch) to read Ref-,
and 11 (0Bh) to read Ref+/2.

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Reading Digital I/O Command

The Read Digital I/O command returns a byte which represents
the states of the 3 digital input and 3 digital output states. Bits 3-5
correspond to the states of digital inputs 0-2. Bits 0-2 correspond to
the states of digital outputs 0-2. If a bit is a 0 then the digital state of
that digital I/O is LOW. If a bit is a 1 then the digital state of the I/O is
HIGH. Refer to Table 3.4 and 3.5.

Command Syntax

!{addr}RD

Unit Response

{states}

Where {states} is a byte in which Bits 0-2 corresponds to the
current states of Digital Outputs 0-2 and Bits 3-5 corresponds to the
current states of Digital Inputs 0-2.

Table 3.4 - Read Digital I/O Response for Outputs

Response Byte Digital Outputs

Bit 2 Bit 1 Bit 0 #2 #1 #0

0 0 0 LOW LOW LOW
0 0 1 LOW LOW HIGH
0 1 0 LOW HIGH LOW
0 1 1 LOW HIGH HIGH
1 0 0 HIGH LOW LOW
1 0 1 HIGH LOW HIGH
1 1 0 HIGH HIGH LOW
1 1 1 HIGH HIGH HIGH

Table 3.5 - Read Digital I/O Response for Inputs

Response Byte Digital Inputs

Bit 5 Bit 4 Bit 3 #2 #1 #0

0 0 0 LOW LOW LOW
0 0 1 LOW LOW HIGH
0 1 0 LOW HIGH LOW
0 1 1 LOW HIGH HIGH
1 0 0 HIGH LOW LOW
1 0 1 HIGH LOW HIGH
1 1 0 HIGH HIGH LOW
1 1 1 HIGH HIGH HIGH

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Set Digital Output Command

The Set Digital Output command is used to set the states of the
3 digital output lines. This command requires a data byte. The data
byte is used to specify the output states. Bits 0-2 correspond to the
states of digital outputs 0-2. If a bit is a 0 then the output will be set
LOW. If a bit is a 1 then the output will be set HIGH. Refer to Table

3.6. NOTE: This command ignores Bits 3-7 of the data byte.
Command Syntax

!{addr}SO{states}

Where {states} is a byte in which Bits 0-2 correspond to the outputs
states of Digital Outputs 0-2
Unit Response

no response

Table 3.6 - Set Digital Output Data Byte Values

Data Byte Digital Outputs

Bit 2 Bit 1 Bit 0 #2 #1 #0

0 0 0 LOW LOW LOW
0 0 1 LOW LOW HIGH
0 1 0 LOW HIGH LOW
0 1 1 LOW HIGH HIGH
1 0 0 HIGH LOW LOW
1 0 1 HIGH LOW HIGH
1 1 0 HIGH HIGH LOW
1 1 1 HIGH HIGH HIGH

Set Module Address Command

The Set Module Address command is used to change the
address of a 485SDA10. This command requires a data byte. The
data byte is used to specify the new address of the unit. The
address of a module is stored in non-volatile memory.
Command Syntax

!{addr}SA{new address}

Response Syntax

no response
Where {addr} is the current address of the module and {new
address} is a byte representing the new address.

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Set Power-up States Command

The Set Power-up States command is used to set the states of
the digital outputs at power-up. This command requires a data byte.
The data byte is used to specify the power-up output states. Bits 0-2
correspond to the power-up states of digital outputs 0-2. If a bit is a
0 then the output will be set LOW at power-up. If a bit is a 1 then
the output will be set HIGH at power-up. Refer to Table 3.6.
NOTE: This command ignores bits 3-7 of the data byte.

Command Syntax

!{addr}SS{states}

Response Syntax

no response

Where {states} is a byte in which Bits 0-2 correspond to the
power-up states of Digital Outputs 0-2

Set Turn-around Delay Command

The Set Turn-around Delay command sets the amount of time
the 485SDA10 waits to respond after executing a command. This
delay is necessary when two RS-485 transmitters are sharing a pair
of wires to ensure that two transmitters are not enabled at the same
time. Refer to B&B Electronics’ free RS-422/RS-485 Application
Note for more information on RS-422/485. The turn-around delay is
stored in non-volatile memory. This command requires a data byte.
The data byte is used to specify the turn-around delay. One unit of
turn-around delay is equal to the transmission time of one character.
The transmission time can be computed as follows:

time = (1 / baud rate) * 10

Command Syntax

!{addr}SC{delay}

Response Syntax

no response

Where {delay} is a byte used to specify the turn-around delay.

Read Module Configuration Command

The Read Module Configuration command reads the
485SDA10’s address, power-up states, and turn-around delay (in
that order).

Command Syntax

!{addr}RC

Response Syntax

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{address}{states}{delay}

Where {address} is a byte representing the module’s current
address, {states} is a byte representing the module’s power-up
states, and {delay} is a byte representing the module’s turn-around
delay.

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Chapter 4 - A/D

This chapter will deal with manipulating an A/D reading and cover
some of the aspects that were not explained in the A/D Connections
chapter.

Sampling Rate

The A/D converter has a conversion time of around 20
microseconds, however the sampling rate is limited by the serial
communications. The maximum sampling rate for a single channel
is around 120 samples per second (9600 baud). This rate drops to
25 samples per second when sampling all of the channels. When
reading an A/D input, the 485SDA10 takes four readings and returns
the average (0.5 and greater are rounded up) of these readings.
This averaging filters out noise.

A/D Input Range

The A/D input range on the 485SDA10 is from 0 to +5V DC. If it
is possible for your device to output a voltage that doesn’t fall in this
range, steps must be taken to ensure that the voltage remains
between 0 and +5V DC. Voltages outside this range will damage
the unit.

Reference Inputs

The A/D reference inputs set the top and bottom of the data
range. A/D Ref Input- sets the bottom of the data range.
A/D Ref Input+ sets the top of the data range. Since these inputs
are directly related to the data range, it is important that a precision
reference is used. The 485SDA10 has a 5V DC +/- 0.5% reference
available. The voltage on A/D Ref Input+ must be at least 2.5V DC
greater than A/D Ref Input-. The voltage difference between
A/D Ref Input+ and A/D Ref Input- is referred to as the Reference
Range.

Reference Range = (A/D Ref Input+) - (A/D Ref Input-)
Typically A/D Ref Input- is connected to Analog ground and
A/D Ref Input+ is connected to +5V DC. Figure 2.1 in Chapter 2
shows the typical connections for a reference range of 0 to 5V DC.

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Data Range

The data range of the A/D converter is determined by
A/D Ref Input+ and A/D Ref Input-. A/D Ref Input- sets the bottom
of the data range. Any input voltage that is less than or equal to the
A/D Ref Input- will be read as a zero. A/D Ref Input+ sets the top of
the data range. Any input voltage that is greater than or equal to the
A/D Ref Input+ will be read as a 1023 (3FFh). The data range is as
follows:

Data Range = (A/D Ref Input-) to (A/D Ref Input+)

Data Range = 0 to 1023

Data Range = 0 to 3FFh

Figure 4.1 shows the Data Range and A/D Ref Inputs relationship.

Figure 4.1 - A/D Converter Data Range

Converting Data

The data read from the 485SDA10 A/D converter is directly
related to the A/D input channel and the reference range (discussed
in previous sections). The 485SDA10 has a 10-bit A/D converter. A
10-bit A/D has 1024 possible output values, 0 to 1023 (0 to 3FFh).
These 1024 output values are divided into equal steps over the
reference range. The size of each step can be computed as follows:

Step size = (Reference Range) / 1023

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The step size is also referred to as the resolution. Once the step
size is known, all that is needed to determine the voltage of an A/D
input is the number of steps. The data returned from the 485SDA10
is the number of steps. The voltage at the A/D inputs can be
calculated as follows:

Voltage = (# of steps) * (Step size)

Example 4.1 - Assume: A/D Ref. Input + = 5.0V DC and A/D
Ref.Input - = 0V DC.
Therefore:

Reference Range = (A/D Ref. Input +) - (A/D Ref. Input -)
Reference Range = (5.0V DC) - (0V DC)
Reference Range = 5.0V DC
Step size = (Reference Range) / 1023
Step size = (5.0V DC) / 1023
Step size = 4.8876 millivolts

Example #1: A/D reading = 1023 (3FFH)

A/D voltage = reading * step size
A/D voltage = 1023 * 4.8876 millivolts
A/D voltage = 5.0 Volts

Example #2: A/D reading = 0

A/D voltage = 0 * 4.8876 millivolts
A/D voltage = 0 Volts

Example #3: A/D reading = 675 (2A3H)

A/D voltage = 675 * 4.8876 millivolts
A/D voltage = 3.2991 Volts

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Chapter 5 - Software

This chapter covers programming techniques such as
constructing a command string, receiving data and manipulating
data. The various steps and examples are shown in QuickBasic. If
you are programming in another language, these sections can be
used as a guideline for programming the 485SDA10.

Read A/D Command

The Read A/D channels command returns two bytes for each
channel read. The two bytes represent the most significant byte
(MSB) and least significant byte (LSB) of the reading. The MSB is
received first, followed by the LSB. This command requires a data
byte. The data byte is used to specify the number of the highest
channel to be read. All channels less than this channel will be read
as well.

The steps to reading an A/D command are given below:

1. Constructing the command string:

Command$ = “!” + CHR$(addr) + “RA” + CHR$(channel)

The value of channel is equal to the highest channel to be
read.

2. Transmitting the command string:

Print #1, Command$;

3. Receiving the data:

MSB$ = INPUT$(1, #1)
LSB$ = INPUT$(1, #1)

4. Manipulating the data:

reading = (ASC(MSB$) * 256) + ASC(LSB$)

The value of reading is the result of the A/D conversion.

5. Repeat Steps 3 & 4 until each channel has been completed.

Example 5.1 - Read A/D channels 1 and 0 of the module with an
address of 5.

channel = 1
addr = 5
Command$ = “!” + CHR$(addr) + “RA” + CHR$(channel)
Print #1, Command$;

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‘Get the value of channel 1

MSB$ = INPUT$ (1, #1)
LSB$ = INPUT$ (1, #1)
reading1 = (ASC(MSB$) * 256) + ASC(LSB$)

‘Get the value of channel 0

MSB$ = INPUT$ (1, #1)
LSB$ = INPUT$ (1, #1)
reading0 = (ASC(MSB$) * 256) + ASC(LSB$)

The value of reading1 is the result of the A/D conversion on
channel 1. The value of reading0 is the result of the A/D conversion
on channel 0.

Read Digital I/O Command

The Read Digital I/O command returns a byte which
represents the states of the 3 digital input and 3 digital output states.
Bits 3-5 correspond to the states of digital inputs 0-2, and bits 0-2
correspond to the states of digital outputs 0-2. If a bit is a 0 then the
digital state of that digital I/O is LOW. If a bit is a 1 then the digital
state of the I/O is HIGH.

The steps to reading a digital I/O command are given below:

1. Constructing the command string:

Command$ = “!” + CHR$(addr) + “RD”

2. Transmitting the command string:

Print #1, Command$;

3. Receiving the data:

Reply$ = INPUT$ (1, #1)

4. Manipulating the data:

states = ASC(Reply$)

5. Determining an I/O’s status

status = states AND mask

6. Repeat Step 5 until the status of each I/O has been
determined.

By “ANDing” the value of states with the appropriate mask of an
I/O line, the status of can be determined. If status is equal to zero
then the I/O line is LOW. If status is not equal to zero then the I/O
line is HIGH. Table 5.1 shows the mask values for each I/O.

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Table 5.1 - Digital I/O Mask Values

Mask Values

I/O Line Hexadecimal Decimal

Digital Output #0 1H 1
Digital Output #1 2H 2
Digital Output #2 4H 4
Digital Input #0 8H 8
Digital Input #1 10H 16
Digital Input #2 20H 32

Example 5.2 - Determining the status of Digital Input #1 of the
module with and address of 10.

mask = &H10
Command$ = “!” + CHR$(addr) + “RD”
Print #1, Command$;
Reply$ = INPUT$ (1, #1)
states = ASC (Reply$)
status = states AND mask

If status is equal to zero then Digital Input #1 is LOW. If status is

not equal to zero then Digital Input #1 is HIGH.

Set Digital Output States

The Set Digital Output command is used to set the states of the
3 digital output lines. This command requires a data byte. The data
byte is used to specify the output states. Bits 0-2 correspond to the
states of digital outputs 0-2. If a bit is a 0 then the output will be set
LOW. If a bit is a 1 then the output will be set HIGH. NOTE: This
command ignores Bits 3-7 of the data byte.

The steps to setting the digital output states are given below:

1) Constructing the command string:
a) Set Appropriate Outputs HIGH

states = states OR mask

By “ORing” the current states with the appropriate
mask of a digital output (given in Table 5.1), the

output’s data bit will be set to a “1” (which will be set
HIGH).

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b) Set Appropriate Outputs LOW

states = states AND (NOT(mask))

By “ANDing” the current states with the complement of
the appropriate mask of a digital output (given in Table

5.1), the output’s data bit will be set to a “0” (which will
be set LOW).

c) Construct the string

Command$ = “!0SO” + CHR$(states)

2) Transmitting the command string:

Print #1, Command$;

Example 5.3 - Set Digital Output #0 HIGH and Digital Output #2

LOW of the module with and address of 5.

addr = 5

‘ Set bit 0 of states to make Digital Output #0 HIGH

states = states OR 1

‘ Clear bit 2 of states to make Digital Output #2 LOW

states = states AND (NOT(4))
Command$ = “!” + CHR$(addr) + “SO” + CHR$(states)
Print #1, Command$;

Digital Output #0 will be set HIGH. Digital Output #2 will be set LOW.
Digital Output #1 will not change. Note that the variable states is
assumed to be value from Example 5.2.

Set Module Address

The Set Module Address command is used to change the
address of a 485SDA10. This command requires a data byte. The
data byte is used to specify the new address of the unit. The
address of a module is stored in non-volatile memory.

The steps to setting a module address are given below:

1) Constructing the command string:

Command$ = “!” + CHR$(addr) + “SO” + CHR$(newaddr)

Where {addr} is the current address of the module and
{new address} is a byte representing the new address.

2) Transmitting the command string:

Print #1, Command$

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Example 5.4 – Change the address of a model from 5 to 10.

addr = 5
newaddr = 10
Command$ = “!” + CHR$(addr) + “SA” + CHR$(newaddr)
Print #1, Command$

Set Power-up States Command

The Set Power-up States command is used to set the states of
the digital outputs at power-up. This command requires a data byte.
The data byte is used to specify the power-up output states. Bits 0-2
correspond to the power-up states of digital outputs 0-2. If a bit is a
0 then the output will be set LOW at power-up. If a bit is a 1 then the
output will be set HIGH at power-up. Refer to Table 3.6.
NOTE: This command ignores bits 3-7 of the data byte.

The steps to setting a module’s power up states are given below:

1) Construct the command string:
a) Set appropriate outputs HIGH

states = states OR mask

By “ORing” the current states with the appropriate
mask of a digital output given in Table 5.1, the output’s

data bit will be set to a “1” (HIGH).

b) Set appropriate outputs LOW

states = states AND (NOT(mask))

By “ANDing” the current states with the complement of
the appropriate mask of a digital output given in Table

5.1, the output’s data bit will be set to a “0” (LOW).

c) Construct the string

Command$ = “!” + CHR$(addr) + “SS” + CHR$(states)

Where addr is the module’s address.

2) Transmitting the command string:

Print #1, Command$

Example 5.5 – Set digital outputs 0 and 1 HIGH and digital output 2

LOW on the module with address 5.

addr = 5
states = 0

‘ Set bit 0 of states to make digital output 0 HIGH

states = states OR 1

‘ Set bit 1 of states to make digital output 1 HIGH

states = states OR 2

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‘ Clear bit 2 of states to make digital output 2 LOW

states = states AND (NOT(4))
Command$ = “!” + CHR$(addr) + “SS” + CHR$(states)
Print #1, Command$

At power-up digital output 0 will be HIGH, digital output 1 will
be HIGH, and digital output 2 will be LOW.

Set Turn-around Delay

The Set Turn-around Delay command sets the amount of time
the 485SDA10 waits to respond after executing a command. This
delay is necessary when two RS-485 transmitters are sharing a pair
of wires to ensure that two transmitters are not enabled at the same
time. Refer to B&B Electronics’ free RS-422/RS-485 Application
Note for more information on RS-422/485. The turn-around delay is
stored in non-volatile memory. This command requires a data byte.
The data byte is used to specify the turn-around delay. One unit of
turn-around delay is equal to the transmission time of one character.
This transmission time can be computed as follows:

time = (1 / baud rate) * 10

The steps to setting a module’s turn-around delay are given below:

1) Constructing the command string:

Command$ = “!” + CHR$(addr) + “SC” + CHR$(delay)

Where addr is the module’s address and delay is the turn­around delay. Refer to Chapter 3 for more information on
turn-around delay.

2) Transmitting the command string:

Print #1, Command$

Example 5.6 – Set the turn-around delay on the module with

address 5 to 100 character transmission times.

addr = 5

delay = 100

Command$ = “!” + CHR$(addr) + “SC” + CHR$(delay)

Print #1, Command$

The module at address 5 will now have a turn-around delay of
100 character transmission times.

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Read Module Configuration

The Read Module Configuration command reads the
485SDA10’s address first, then the power-up states, and finally the
turn-around delay.

The steps to reading a module’s configuration are given below:

1) Constructing the command string:

Command$ = “!” + CHR$(addr) + “RC”

Where addr is the module’s address.

2) Transmitting the command string:

Print #1, Command$

3) Receiving the address data:

Reply$ = INPUT$(1,#1)

4) Determining the address:

address = ASC(Reply$)

5) Receiving the power-up states data:

Reply$ = INPUT$(1,#1)

6) Determining the power-up states:

states = ASC(Reply$)

Refer to Read Digital I/O earlier in this chapter for the steps to
determine the status of individual output states.

7) Receiving the turn-around delay data:

Reply$ = INPUT$ (1,#1)

8) Determining the turn-around delay:

delay = ASC(Reply$)

Example 5.7 – Determining the configuration of the module with an

address of 10.

addr = 10

Command$ = “!” + CHR$(addr) + “RC”

Print #1, Command$

‘ Determine the module’s address

Reply$ = INPUT$ (1,#1)

address = ASC(Reply$)

‘ Determine the module’s power-up states

Reply$ = INPUT$ (1,#1)

states = ASC(Reply$)

‘ Determine the module’s turn-around delay

Reply$ = INPUT$ (1,#1)

delay = ASC(Reply$)

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Appendix A: Adding Data Field Confirmation

With serial communications in a laboratory environment, the
possibility of a communication error occurring is minimal. However,
in a harsh or an industrial environment the possibility increases. A
communication error occurs when a bit transmitted as a “1” is
received as a “0” or vice versa. If the 485SDA10 receives an error
in one or more of the first four command characters (“!0xx”), the unit
will not execute the command. However, if the 485SDA10 receives
a communication error on a data byte (channel byte for Read Analog
command or state byte for Set Output State command), the
command will be executed since the unit has no way of knowing that
there was an error.

To provide the 485SDA10 with a way of detecting errors in the
data fields, an additional set of commands can be used. This set of
commands begins with the “#” (23h) character, instead of the “!”
(21h) character. Refer to Table A-1. With these commands every
data byte that is transmitted or received is followed by its
complement.

Example A.1 - To read A/D channel zero:

Command syntax:

#{addr}RA{00}{FF}

Response syntax:

{ch0 msb}{~ ch0 msb}{ch0 lsb} {~ ch0 lsb}

Where “~” is used to indicate the “complement of.”

If A/D channel 0 has a reading of 1, the following would be
received:

{00}{FF}{01}{FE}

Where FFh is the complement of 0 and FEh is the complement
of 1. The complement of number “x” can be calculated in
QuickBasic as follows:

comp = (NOT x) AND &HFF

485SDA103798 Manual Appendix A A-1

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Table A-1 Extended Commands

Function Command Response
Read A/D Channels #{addr}RA{x}{~x} {chxmsb}{~chxmsb}{chxlsb}

{~chxlsb}{ch(x-1)msb}...
{ch0msb}

{~ch0msb}{ch0lsb}{~ch0lsb}
Read Digital I/O #{addr}RD {I/O states}{~I/O states}
Set Output States #{addr}SO{x}{~x} no response
Set Module
Address
Set Power-up
States
Set Turn-around
Delay
Read Configuration #{addr}RC {addr}{~addr}{powerup

#{addr}SA{new
addr}{~new addr}
#{addr}SS{x}{~x} no response

#{addr}SC{x}{~x} no response

no response

states}{~powerup

states}{turn-around

delay}{~turn-around delay}

Where “x” is the required data byte and “~” signifies the complement
of the specified byte.

A-2 Appendix A 485SDA103798 Manual

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Appendix B: Analog Input Impedance

=

≤

Ω

When interfacing with an A/D converter, it is important that the
device you are connecting can drive the A/D input. To determine if
your device can drive an A/D input, there are three factors you must
consider:

• Output impedance of the device

• Input impedance of A/D

• A/D sampling time

The goal is to have the voltage at the A/D input settle to a voltage
close to the output voltage of the device in a time frame that is less
than the A/D sampling time. (Close to means a value significantly
less than the resolution of the A/D). If the voltage does not settle
fast enough, errors will occur in the reading, resulting in a loss of
resolution.

The next section, titled “Simplified Analog Input Analysis,”
contains information from Texas Instruments data sheet on the
TLC1543. The TLC1543 is the A/D converter that is used on the
485SDA10. This section provides a simplified calculation which can
be used to determine the maximum output impedance the device
can have to settle the A/D input to a voltage within one half LSB.

For the 485SDA10:

t us

100

c

Using this information:

R k

170

s

If the output impedance of your device is 170kΩ, you should figure
an additional error of ½ LSB.

It should be pointed out that this is a simplified analysis and
there other several other factors that must be considered (pin
capacitance, noise immunity, etc.). The data sheet for the TLC1543
states that “The driving source impedance should be less than or
equal to 1kΩ.” B&B Electronics recommends placing a voltage
follower between the 485SDA10 and any device with output source
impedance greater than 1kΩ.

485SDA103798 Manual Appendix B B-1

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Simplified Analog Input Analysis

=

+

=

−

−

=××

=+×

×

Ω

Using the equivalent circuit in Figure B-1, the time required to
charge the analog input capacitance from 0 to Vs within ½ LSB can
be derived as follows:

The capacitance charging voltage is given by

t RC

V V

= −−( )1 (1)

c s

where

R R r

t s i

The final voltage to ½ LSB is given by

V LSB V V

( ) ( )1 2 2048

c s s

Equating equation 1 to equation 2 and solving for time tc gives

V V V e

− = −

( ) ( )2048 1 (3)

s s s

and

t LSB R C

( ) ln( )1 2 2048

c t i

Therefore, with the values given the time for the analog input signal
to settle is

t LSB R

( ) ( ) ln( )1 2 1 60 2048

c s

This time must be less than the converter sample time shown in the
timing diagrams.

e

c t i

t RC

c t i

k pF

(5)

(2)

(4)

VI = Input Voltage at A0 - A10
VS = External Driving Source Voltage
RS = Source Resistance
ri = Input Resistance
Ci = Equivalent Input Capacitance

*Driving source requirements:

• Noise and distortion for the source must be
equivalent to the resolution of the converter.

• RS must be real at the input frequency.

B-2 Appendix B 485SDA103798 Manual

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Figure B-1. Equivalent Input Circuit Including the Driving Source

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Appendix C: Decimal to HEX to ASCII Table

Table C-1: Decimal to HEX to ASCII Table

DECIMAL to HEX to ASCII CONVERSION TABLE

DEC HEX ASCII KEY DEC HEX ASCII DEC HEX ASCII DEC HEX ASCII

0 0 NUL ctrl @ 32 20 SP 64 40 @ 96 60 `
1 1 SOH ctrl A 33 21 ! 65 41 A 97 61 a
2 2 STX ctrl B 34 22
3 3 ETX ctrl C 35 23 # 67 43 C 99 63 c
4 4 EOT ctrl D 36 24 $ 68 44 D 100 64 d
5 5 ENQ ctrl E 37 25 % 69 45 E 101 65 e
6 6 ACK ctrl F 38 26 & 70 46 F 102 66 f
7 7 BEL ctrl G 39 27 ' 71 47 G 103 67 g
8 8 BS ctrl H 40 28 ( 72 48 H 104 68 h

9 9 HT ctrl I 41 29 ) 73 49 I 105 69 i
10 A LF ctrl J 42 2A * 74 4A J 106 6A j
11 B VT ctrl K 43 2B + 75 4B K 107 6B k
12 C FF ctrl L 44 2C , 76 4C L 108 6C l
13 D CR ctrl M 45 2D - 77 4D M 109 6D m
14 E SO ctrl N 46 2E . 78 4E N 110 6E n
15 F SI ctrl O 47 2F / 79 4F O 111 6F o
16 10 DLE ctrl P 48 30 0 80 50 P 112 70 p
17 11 DC1 ctrl Q 49 31 1 81 51 Q 113 71 q
18 12 DC2 ctrl R 50 32 2 82 52 R 114 72 r
19 13 DC3 ctrl S 51 33 3 83 53 S 115 73 s
20 14 DC4 ctrl T 52 34 4 84 54 T 116 74 t
21 15 NAK ctrl U 53 35 5 85 55 U 117 75 u
22 16 SYN ctrl V 54 36 6 86 56 V 118 76 v
23 17 ETB ctrl W 55 37 7 87 57 W 119 77 w
24 18 CAN ctrl X 56 38 8 88 58 X 120 78 x
25 19 EM ctrl Y 57 39 9 89 59 Y 121 79 y
26 1A SUB ctrl Z 58 3A : 90 5A Z 122 7A z
27 1B ESC ctrl [ 59 3B ; 91 5B [ 123 7B {
28 1C FS ctrl \ 60 3C < 92 5C \ 124 7C |
29 1D GS ctrl ] 61 3D = 93 5D ] 125 7D }
30 1E RS ctrl ^ 62 3E > 94 5E ^ 126 7E ~
31 1F US ctrl _ 63 3F ? 95 5F _ 127 7F DEL

“

66 42 B 98 62 b

485SDA103798 Manual Appendix C C-1

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FEDERAL COMMUNICATIONS COMMISSION
RADIO FREQUENCY INTERFACE STATEMENT

Class A Equipment

This equipment has been tested and found to comply with the
limits for Class A digital device, pursuant to Part 15 of the FCC
Rules. These limits are designed to provide reasonable protection
against harmful interference when the equipment is operated in a
commercial environment. This equipment generates, uses, and can
radiate radio frequency energy and, if not installed and used in
accordance with the instructions, may cause harmful interference to
radio communications. Operation of this equipment in a residential
area is likely to cause harmful interference, in which case the user
will be required to correct the interference at personal expense.

FCC Class A Equipment Statement