B&B Electronics 232DTT User Manual

Digital Thermometer & Thermostat

with RS-232 Interface

Model 232DTT

Document No. 232DTT1795

B&B Electronics Mfg. Co. Inc.

P.O. Box 1040 -- Ottawa, IL 61350

PH [phone] -- FAX [phone]

Internet:

http://www.bb-elec.com

[e-mail]

[e-mail]

B&B Electronics -- April 1995

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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 Table of Contents

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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

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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 non­volatile 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. T

user programmed TH register.

2. T

the user programmed TL register.

3. T

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.

- Turns on when the temperature equals or exceeds the

HIGH

- Turns on when the temperature is equal to or less than

LOW

- Turns on when the temperature equals or exceeds the

COM

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.

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+12VDC

DTT OUTPUT

TCOM

GND

12VDC
RELAY
COIL

RELAY
CONTACT

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.

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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.

Table 2. Temperature/Data Relationships

Temperature DTT output hex value dec value

+125° C
+25° C
1/2° C
0° C

-1/2° C

-25° C

-55° 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.

0 11111010 00 FAh 250
0 00110010 00 32h 50
0 00000001 00 01h 1
0 00000000 00 00 h 0
1 11111111 01 FFh 511
1 11001110 01 CEh 462
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

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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

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again. After sending the Set High Thermostat command, delay for at
least 10 ms to allow the DTT to program the register.

Set Low Thermostat

Command: !0SL
Arguments: 9 bit, two’s complement value to set non-volatile TL

register.

Response: none
Dec. Example: !0SL<0><33>
ASCII Example: !0SL<NUL >!
Description: Sending the decimal arguments 0 (ASCII NUL) and 33

(ASCII !) sets the TL register to a temperature of 16.5 ° C. This is a
non-volatile register and will not change until this command is issued
again. After sending the Set Low Thermostat command, delay for at
least 10 ms to allow the DTT to program the register.

Table 4. Command Summary

Function Command Argument Return Value

read temperature !0RT none 9 bit, 2’s comp.
read status register !0RS none byte
read high thermostat !0RH none 9 bit, 2’s comp.
read low thermostat !0RL none 9 bit, 2’s comp.
clear status register !0SC none none
set high thermostat* !0SH 9 bit, 2’s comp. none
set low thermostat* !0SL 9 bit, 2’s comp. none

*NOTE: After “programming” the 232DTT, there is approximately
10ms of down time when the unit will not respond. Do not attempt to
communicate with the DTT for at least 10ms after programming the
thermostat registers.

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Chapter 5. Software

There is both a DOS program (DTT_DOS.EXE) and a
Windows program (232DTT_W.EXE) which allow you to read the
current temperature in either Fahrenheit or Celsius, as well as set
the upper and lower thresholds.

Installation

To install on your hard drive follow these steps:

• Place the disk in drive A.

• Type A: and press the ENTER key.

• Type INSTALL and press the ENTER key.

Windows Setup

After the software is installed on your hard disk, the
following files should be located in the 232DTT directory:
232DTT_W.EXE, VBRUN300.DLL, and MSCOMM.VBX.

To set up the 232DTT under windows follow the following steps:

1. Run Windows.

2. Select the “FILE” menu under the Program Manager.

3. Select the “NEW” option.

4. From the “New Program Object” window select “Program Item”

option and then select “OK”.

5. From the “Program Item Properties” window:

a) Type in the “Description” box:

232DTT

b) Type in the “Command Line” box:

C:\232DTT\232DTT_W.EXE

6. From the “Program Item Properties” menu select the “OK”

option.

Setup of the 232DTT is now complete. The 232DTT icon should
now appear in the current window. Simply double click on the icon
to execute the program.

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Appendix A. Using SimpTerm

B&B Electronics shareware terminal program, SimpTerm, is
included on the DTT floppy disk. SimpTerm is a powerful
troubleshooting tool which will allow you to communicate through up
to four serial ports at any address or interrupt. You will need to know
the address and interrupt of the serial port that the DTT is connected
to.

To use SimpTerm to communicate with the DTT, follow the
instructions to open the port connected to the DTT.

1. Raise RTS and DTR to power the DTT, or connect an external

power supply.

2. Check that the baud rate is set anywhere from 1200 - 9600

baud.

3. Type the following command, the second character is a zero, all

commands must be in capital letters: !0RT

4. The DTT will respond with two characters indicating

temperature. Room temperature is usually NUL followed by a
character close in the ascii table to a comma. A NUL is indicated
by <0>.

5. To set the TH register to 25° C, follow, type the following:

!0SH<0>2. The decimal value of the ASCII 2 is 50. This
corresponds to 25° C. The NUL indicates that it is to be a
positive value.*

6. To read back the value stored in the TH register, type the

following command: !0RH. If step 5 has been successfully
completed the DTT will respond with <0>2.

* The <0> is actually a NUL character and is not represented by a
keyboard key. SimpTerm allows these characters to be transmitted
using the following procedure:

Hold down the ALT key, type the decimal value (two digits) on the
numeric keypad and release the ALT key. For example, the NUL is
transmitted by: ALT 00 [release ALT].

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Appendix B. Decimal/ASCII Table

DECIMAL to HEX to ASCII CONVERSION TABLE

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

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 66 42 B 98 62 b
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

232DTT 1795 Manual Appendix B B-1

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