B&B Electronics 232DTT User manual

232DTT1795 Manual Cover Page
B&B Electronics -- PO Box 1040 -- Ottawa, IL 61350
PH [phone] -- FAX [phone]
B&B Electronics Mfg. Co. Inc.
P.O. Box 1040 -- Ottawa, IL 61350
PH [phone] -- FAX [phone]
Internet:
http://www.bb-elec.com
[email protected]
[email protected]
B&B Electronics -- April 1995
Digital Thermometer & Thermostat
with RS-232 Interface
Model 232DTT
Document No. 232DTT1795

232DTT1795 Manual Table of Contents
B&B Electronics -- PO Box 1040 -- Ottawa, IL 61350
PH [phone] -- FAX [phone]
TABLE OF CONTENTS
CHAPTER 1. GENERAL INFORMATION.................................. 1
INTRODUCTION............................................................................... 1
FEATURES..................................................................................... 1
PACKING LIST................................................................................ 1
SPECIFICATIONS ............................................................................ 1
RS-232 CONNECTIONS.................................................................. 2
CHAPTER 2. 232DTT FUNCTIONS.......................................... 3
DIGITAL THERMOMETER ................................................................. 3
PROGRAMMABLE THERMOSTAT ...................................................... 3
CHAPTER 3. 232DTT DATA FORMAT..................................... 5
CHAPTER 4. 232DTT COMMANDS.......................................... 7
READ TEMPERATURE ..................................................................... 7
READ STATUS................................................................................ 7
READ HIGH.................................................................................... 8
READ LOW .................................................................................... 8
CLEAR STATUS REGISTER.............................................................. 8
SET HIGH THERMOSTAT................................................................. 9
SET LOW THERMOSTAT.................................................................. 9
CHAPTER 5. SOFTWARE....................................................... 11
INSTALLATION .............................................................................. 11
WINDOWS SETUP ........................................................................ 11
APPENDIX A. USING SIMPTERM..........................................A-1
APPENDIX B. DECIMAL/ASCII TABLE.................................B-1

232DTT1795 Manual Chapter 1 1
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Chapter 1. General Information
Introduction
The 232DTT is a digital thermometer and thermostat which
operates through an RS-232 interface. Non-volatile registers hold
programmable high and low thermostat settings. Current
temperature is reported by polling the DTT, while thermostat
operations continue as long as the unit is powered.
Features
• ±0.5 °C accuracy and resolution
• High, low and hysteresis type thermostat outputs
• Port-powered from host RS-232 port (RTS & DTR high)
• Thermostat thresholds programmable in non-volatile registers
• Status Register latches if thermostat outputs have tripped
Packing List
Examine the shipping carton and contents for physical
damage. The following items should be in the shipping carton:
1. 232DTT unit
2. One 232DTT 3.5” disk
3. This instruction manual
If any of these items are damaged or missing, contact B&B
Electronics immediately.
Specifications
Communications:
Standard: RS-232 (unit is DCE)
Baud Rate: 1200 to 9600 (automatic detection)
Format: 8 data bits, 1 stop bit, no parity
Connector: DB-25S (female)
Thermometer Error
±0.5 °C from 0 - 70°C
(±0.9 °F from 32 - 158°F)
±1 °C from -40 °C to 0 °C and 70 °C to 85 °C *
(±1.8 °F from -40 °F to 32 °F and 158 °F to 185 °F)
* The 232DTT is guaranteed to operate from 0-70 °C.

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Thermometer Resolution
0.5 °C (0.9 °F)
Temperature Conversion Time
1 second
Open Collector Thermostat Outputs
Low (on) voltages: 1.2VDC @ 100 mA max.
High (off) voltages: 40VDC max.
Power Supply
Port powered with RTS and DTR outputs set high
External power: 12VDC @ 30mA
NOTE: When using an external supply, the supply should be
connected only to specifically labeled power inputs (power
jack, terminal block, etc.). Connecting an external power supply
to the handshake lines may damage the unit. Contact technical
support for more information on connecting an external power
supply to the handshake lines.
RS-232 Connections
The 232DTT communicates using pins 2, 3, and 7 (TD, RD
and GND). However, power is drawn from the handshake lines RTS
(pin 4) and DTR (pin 20). These connections must be present to
power the unit.
Table 1. RS-232 Pinouts
Signal Pin
TD 2
RD 3
RTS 4
GND 7
DTR 20

232DTT1795 Manual Chapter 2 3
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Chapter 2. 232DTT Functions
Digital Thermometer
The 232DTT continuously measures temperature, with a
new measurement completed once per second. When a Read
Temperature command is received, the DTT immediately reports
back the result of the last measurement completed.
Programmable Thermostat
The 232DTT also functions as a thermostat. Two non-
volatile registers can be programmed. The high threshold register,
TH, is programmed using the !0SH command. The low threshold
register, TL, is programmed using the !0SL command. A complete
command description can be found in Chapter 4. Thermostat
operation is a continuous background function. As long as the unit is
powered, the thermostat outputs will be serviced.
Three open collector outputs provide thermostatic controls.
These outputs are current sinking (low) when on, high impedance
(high) when off.
1. THIGH - Turns on when the temperature equals or exceeds the
user programmed TH register.
2. TLOW - Turns on when the temperature is equal to or less than
the user programmed TL register.
3. TCOM - Turns on when the temperature equals or exceeds the
TH register and turns off when the temperature is equal to or
less than the TL register. This output allows the user to program
any amount of hysteresis.
Remember, these are open collector outputs. They do not
source any current (similar to a contact closure to ground). For
example, to drive a relay with a 12VDC coil with the TCOM output,
connect as follows:
1. Connect +12Vdc to one side of the relay coil.
2. Connect the other side of the coil to the TCOM output.
3. Connect the ground of the 12V supply to the GND terminal
block.

4Chapter 2 232DTT1795 Manual
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Figure 1. Relay Output Connection
When connecting a mechanical relay coil, or any inductive
load to the DTT outputs, a reverse bias diode must be connected
across the load to protect the DTT output against large voltages
caused by the inductive load.
The DTT outputs can handle a maximum voltage of 40V
and a maximum current of 100mA. Do not use a relay with coil
ratings exceeding these values.
+12VDC
12VDC
RELAY
COIL
DTT OUTPUT
GND
TCOM
RELAY
CONTACT

232DTT1795 Manual Chapter 3 5
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Chapter 3. 232DTT Data Format
The DTT uses 9-bit, two’s complement format to represent
temperature data. The ninth bit is the sign bit. If this bit is a 0, the
temperature is above 0°C. If the bit is 1, the temperature is less
than 0°C. Each bit represents 1/2°C.
Two’s complement format provides a way for digital devices
to handle negative numbers. To convert the two’s complement value
to a meaningful number representing temperature, follow these
steps:
1. Check bit nine. In our case this is the entire first character. If the
character is decimal 0 (NUL), then the value in the second
character is positive and no further complementing is necessary,
go to step 6. If character is decimal 1, then continue with step 2.
2. Use the NOT function of your programming language to invert
(or complement) the value in the second character.
3. We need to insure that we are only dealing with an eight bit
variable. You may be able to define this in your programming
language. To be sure, we can use the AND function to limit our
new value to only eight bits by ANDing the value from step 2
with FFh. This masks off all but the lowest eight bits.
4. Add a 1 to the value from step 3. This completes the two’s
complement portion of the conversion.
5. Multiply our new value by -1. This simply adds the “-” sign to our
temperature reading.
Table 2. Temperature/Data Relationships
Temperature DTT output hex value dec value
+125°C 0 11111010 00 FAh 250
+25°C 0 00110010 00 32h 50
1/2°C 0 00000001 00 01h 1
0°C 0 00000000 00 00 h 0
-1/2°C 1 11111111 01 FFh 511
-25°C 1 11001110 01 CEh 462
-55°C 1 10010010 01 92h 402

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6. To convert to Celsius, divide by two.
7. To convert to Fahrenheit, multiply the Celsius value by 9; divide
the result by 5; then add 32.
In the BASIC language, these steps look like this:
‘DTT data has been stored in CHAR1$ and CHAR2$
negative = ASC(CHAR1$) ‘ASCII val of sign char (1 or 0)
reading = ASC(CHAR2$) ‘ASCII val of reading
IF negative = 1 THEN
reading = NOT reading ‘invert all bits (complement)
reading = reading AND &HFF ‘limit variable to 8 bits
reading = reading + 1 ‘finish complement procedure
reading = reading * -1 ‘multiply by -1 to add minus sign
END IF
Ctemp = reading / 2 ‘Celsius temperature
Ftemp = (9 * C temp / 5) + 32 ‘Fahrenheit temperature

232DTT1795 Manual Chapter 4 7
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Chapter 4. 232DTT Commands
The DTT commands can be issued from a program, or even
typed in from a simple terminal program. Two files are included on
the 232DTT disk to help learn the DTT commands. A sample
program with source code written in QuickBASIC 4.5 demonstrates
all DTT functions and a simple terminal program is also included. In
addition, a simple data logging utility is provided which allows data to
be logged to a file. Appendix A demonstrates how to communicate
with the DTT from the terminal program. A decimal/ASCII
conversion table is included in Appendix B.
Read Temperature
Command: !0RT
Arguments: none
Response: temperature reading in 9 bit two’s complement format
(shown in boldface)
Dec. Example: !0RT<0><46>
ASCII Example: !0RT<NUL>.
Description: The decimal 0 (NUL) followed by decimal 46,
equivalent to an ASCII “.” converts to a temperature of +23°C.
Read Status
Command: !0RS
Arguments: none
Response: contents of 8 bit status register (shown in boldface)
Dec. Example: !0RS<0><66>
ASCII Example: !0RS<NUL>B
Hex. Example: !0RS<0><42>(since this is an eight bit register, it
may be helpful to use hex representation)
Description: The first character (NUL) has no meaning in this
response. Bit 1 is set, indicating normal operation. Bit 5 is clear
indicating the low thermostat has not tripped. Bit 6 is set, indicating
THIGH has tripped since the last !0SC command.
Table 3. Status Register Description
Bit 0 X (don’t care)
Bit 1 operation
Bit 2 X
Bit 3 X
Bit 4 X
Bit 5 Low Thermostat Tripped Flag
Bit 6 High Thermostat Tripped Flag
Bit 7 X

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Read High
Command: !0RH
Arguments: none
Response: contents of TH register in 9 bit two’s complement format
(shown in boldface)
Dec. Example: !0RH<0><50>
ASCII Example: !0RH<NUL>2
Description: The TH register contains decimal 0 (ASCII NUL) and
decimal 50 (ASCII 2). This converts to a temperature of 25 °C.
When the current temperature is ≥25°C, the high thermostat output
(THIGH) will turn on.
Read Low
Command: !0RL
Arguments: none
Response: contents of TL register in 9 bit two’s complement format
(response is shown in boldface)
Dec. Example: !0RL<0><36>
ASCII Example: !0RL<NUL>$
Description: The TL register contains decimal 0 (ASCII NUL) and
decimal 36 (ASCII $). This converts to a temperature of 18 °C.
When the current temperature is ≤18°C, the low thermostat output
(TLOW) will turn on.
Clear Status Register
Command: !0SC
Arguments: none
Response: none
Example: !0SC
Description: The Clear Status command resets the DTT. Bits 5 and
6 which latch the thermostat outputs are cleared if the current
temperature is within the bounds of TH and TL.
Set High Thermostat
Command: !0SH
Arguments: 9 bit, two’s complement value to set non-volatile TH
register.
Response: none
Dec. Example: !0SH<0><64>
ASCII Example: !0SH<NUL>@
Description: Sending the decimal arguments 0 (ASCII NUL) and 64
(ASCII @) sets the TH register to a temperature of 32°C. This is a
non-volatile register and will not change until this command is issued