dataTaker - Data Loggers, Powerful and Flexible Data Acquisition & Data Logging Systems

The RS232 COMMS Serial Interface

The dataTaker data loggers communicate with a host computer via the RS232 COMMS serial interface. The interface is configured to the RS232 serial interface standard, and is implemented as a 9 pin female D connector for all dataTaker models.

The RS232 COMMS serial interface of all dataTaker Series2 and Series 3 models is electrically isolated to 500 Volts, which provides for protection from damaging electrical currents passing between the host computer and the logger reduces interference from electrical noise eliminates the possibility of host computer to logger ground loops being established which will cause erroneous analog measurements

Note: The RS232 COMMS serial interface of dataTaker Series1 models is not normally electrically isolated, however can be isolated by modifying the communications cable (see below).

The RS232 COMMS serial interface of the dataTakers supports 300, 1200, 2400, 4800 and 9600 baud rates. The communications baud rate is set by the Baud Rate switches of the DIP switch (see below).

Communication parameters for the RS232 COMMS serial interface are permanently set to 8 data bits, 1 stop bit, and no parity.

RS232 COMMS Serial Interface Connector

The RS232 COMMS serial interface of the dataTaker has a female 9 pin D connector. The connector is labelled RS232 COMMS. Pin assignment for the RS232 COMMS serial interface connector of the dataTaker is illustrated in Figure 12 below

 

 

Figure 12 ñ RS232 COMMS Serial Interface Connector Pin Assignments

    (Viewed looking at face of connector)

 

RS232 COMMS Serial Interface - dataTaker Series 1 Only

The RS232 COMMS interface of Series 1 dataTaker models is not electrically  isolated. For most applications the serial interface does not need to be electrically isolated.

The serial interface is normally powered from the internal power supply of the dataTaker by installing links on the back of the dataTaker connector of the communications cable as follows

a link must be installed between pin 2 (dataTaker ground) and pin 1 (serial interface ground) of the 9 pin connector

a link must be installed between pin 7 (dataTaker internal 6 Volt power supply ) and pin 5 (serial interface power input) of the 9 pin connector

The communications cable supplied with the dataTaker has these links installed.

The links on the communications cable connector for powering the serial interface from the dataTaker power supply are shown below in Figures 14 and 15.

Isolating the RS232 COMMS Serial Interface - dataTaker Series 1 Only

The RS232 COMMS serial interface of Series 1 dataTakers can be electrically isolated from the remainder of the dataTaker circuitry. This may be done for a number of reasons including

to protect the host computer from any damaging voltages accidentally applied to the logger channels

to reduce effects of electrical noise on the communications link

to eliminate ground loops between the host computer ground and the data logger ground will cause erroneous analog measurements

The receiver output and the transmitter input to the serial interface circuits are both optically coupled to the remainder of the dataTaker circuitry.

In order to maintain electrical isolation of the serial interface from the remainder of the dataTaker, the serial interface must be powered from an external power supply. The dataTaker and the serial interface must not share the same ground.

Isolation is achieved by removing the powering links installed on the back of the dataTaker connector of the communications cable (see above), and providing power to the interface from an external source.

The schematic for isolating and externally powering the serial interface of the dataTaker is illustrated in Figure 13 below.

 

 

Figure 13 ñ Externally Powering the RS232 COMMS Serial Interface
of dataTaker Series 1 Loggers

 

The dataTaker RS232 COMMS serial interface requires a power supply of 5 to 12 Volts DC at 20 mA. An external power supply for the serial interface is connected as follows

the +ve line from the external power supply is connected to pin 5 (serial interface power input) of the 9 pin connector

the ñve line from the external power supply is connected to pin 1 (serial interface ground) of the 9 pin connector

Reverse polarity protection for externally powering the serial interface is provided by a series diode on pin 5. The negative rail required for the RS232 signal voltage swings is generated by a DCñDC converter within the isolated section of the serial interface.

External power for the serial interface is usually supplied via an extra wire pair in the communication cable. The power requirement of the serial interface is dependent on the transmission speed and distance. However +6 Volts at 20 mA is sufficient for most communications. An asserted Request To Send (RTS) line for many computers is able to supply this power requirement.

Communications Cable

The communications cable supplied with the dataTaker is used to connect a computer to the logger. The cable is wired to suit Windows computers which have a 9 pin serial interface connector.

Some notebook computers now are supplied without any RS232 serial interfaces. In this case an RS232 serial interface can be provided via a USB to RS232 adaptor, or via a docking module.

Older style Windows computers may have a 25 pin connector on the COM port. There is a cable schematic below for these computers.

Cable Type

The use of shielded communications cables is recommended where the cables are long, or where environmental electrical noise is likely to be high. If a shielded cable is used, the shield should be connected to the Frame Ground or Ground pin of the computer serial interface connector.

Short communications cables do not need to be shielded, and can be of any conveniently available cable type.

Long Cables

The RS232 communications standard specifies a maximum cable length of 15 metres (17 yards). However longer cables can be used, and lengths up to 150 metres (170 yards) are possible.

The limitation of communications cable length is determined by cable resistance and capacitance, the level of local electrical noise, the communications baud rate, and the sensitivity of the host serial interface receiver. Longer cables usually require a lower baud rate.

Communications Cable for Windows Computers

Communication cable schematics are illustrated in the following Figures for Windows computers with 25 pin and 9 pin COM port connectors.

 

 

Figure 14a ñ RS232 Communications Cable for Windows Computers
with 25 pin COM Port Connectors

 

Figure 14b ñ RS232 Communications Cable for Windows Computers
with 9 pin COM Port Connectors

 

Communication Cable for Apple Macintosh Computers

Apple Macintosh computers have an RS422 serial interface with a female 8 pin Mini DIN connector, mounted in the rear panel of the computer. This interface can also be used as an RS232 serial interface.

A communications cable wiring schematic for connecting an Apple Macintosh series computer with the dataTaker is shown in Figure 15 below.

Figure 15 also details the 8 pin Mini DIN interface connector of the Apple Macintosh series computers. A communication cable for the Macintosh computers is available from your dataTaker supplier.

 

 

Figure 15 ñ RS232 Communications Cable for Apple Macintosh Computers

 

RS232 Control and Handshake Lines

The RS232 COMMS serial interface of the dataTaker does not support hardware handshake lines (RTS, CTS, DSR, DCD, DTR, etc.).

Setting the RS232 Communications Parameters

All dataTaker data loggers are shipped with the communications parameters for the RS232 COMMS serial interface pre-set to the following settings

ñ 9600 baud
– no parity checking
– 8 data bits
– 1 stop bit

The communications baud rate of the dataTaker is set by the Baud Rate switches of the DIP switch to 300, 1200, 2400, 4800 or 9600 baud.

The communication parameters of the RS232 COMMS serial interface are permanently set to 8 data bits, 1 stop bit, and no parity checking. These settings suit all types of host computers, and cannot be changed.

The Baud Rate

Whenever the host computer or terminal and the dataTaker are communicating, they must transmit and receive information at compatible rates. The receiver of each device must be able to receive information at the rate at which the other device is transmitting the information.

The rate of information transfer between two communicating devices is referred to as the baud rate, and is defined in terms of the number of pulses or bits of information transferred per second. The baud rates must be the same for each direction of data transfer.

The dataTaker models support baud rates of 300, 1200, 2400 and 9600 baud

The choice of baud rate for serial communication with the host computer depends on a number of parameters

the length of communications cable

the level of local electrical noise

the sensitivity of the computer interface receiver

At lower baud rates the maximum scanning rate of the analog input channels by the dataTaker will be reduced if the data is returned as the channels are scanned. This is because of the priority to transmit acquired data to the host rather than to commence a new scan (See Section III ñ Priorities for Returning and Logging Data).

In general practice a baud rate of 9600 baud should be used.

The baud rate of the dataTaker is set by the Baud Rate switches of the DIP switch. The baud rate settings available are illustrated in Figures 16 and 17 below.

The host computer must be set to the same baud rate as the dataTaker. DeTransfer and DeLogger have automatic baud rate matching, and will set the baud rate of the computer to that of the dataTaker when connection is being made or requested.

The Number of Data Bits 

The dataTaker transfers all information as ASCII characters. Each ASCII character is represented by a unique series of data bits, or a bit pattern, comprised of 0's and 1's (See Appendix A - ASCII Character Table).

The ASCII character codes may be made up of 7 or 8 data bits. For example the ASCII representation of the character Z is 1011010 as 7 bit code, and 01011010 as 8 bit code.

Whenever the host computer and the dataTaker are communicating, both devices must transmit and receive the ASCII characters in compatible formats. In order to achieve this compatibility, both devices must be set to represent ASCII characters either as 7 or 8 bit code. This is referred to as the number of data bits.

The RS232 COMMS serial interface of the dataTaker is permanently set to 8 data bits. DeTransfer and DeLogger automatically set the computer to 8 data bits.

Parity Checking

Parity checking provides a means for error checking each ASCII character as it is received by a communicating device. If parity checking is enabled, a bit of 0 or 1 is added after the last bit of the ASCII character. The parity bit is set according to the number of 1's in the ASCII character, and can be defined to return 0 for an odd number of 1's (odd parity) or 0 for an even number of 1's (even parity).

When two devices are communicating, they must both be set for the same parity checking. This enables the receiving device to interpret the parity bit sent by the transmitting device.

The RS232 COMMS serial interface of the dataTaker has the parity checking permanently disabled. DeTransfer and DeLogger automatically set the computer to no parity checking.

The Number of Stop Bits

The stop bits are added to each character by the transmitting device, following the parity bit if parity checking is enabled, or following the last data bit if parity checking is disabled. The stop bits provide a means of character synchronization between the transmitting device and the receiving device. The number of stop bits can usually be set to 1 or 2.

The RS232 COMMS serial interface of the dataTaker is permanently set for 1 stop bit. DeTransfer and DeLogger automatically set the computer to 1 stop bit.

The Baud Rate DIP Switches

The baud rate for the dataTaker RS232 COMMS serial interface is set by the Baud Rate switches of the DIP switch. The DIP switch of the dataTaker is accessed by removing the top cover of the logger.

The range of baud rates available for the RS232 COMMS serial interface, and their selection, is illustrated in Figure 16 & 17 below

 

 

Figure 16 ñ The RS232 COMMS Baud Rate DIP Switch - dataTaker 50

 

 

Figure 17 ñ The RS232 COMMS Baud Rate DIP Switch - dataTaker 500/600 Series

 

The factory setting for the Baud Rate is 9600 baud.

The Baud Rate switches are read periodically, and so if the baud rate is altered while the dataTaker is operating, the change has an immediate effect.

Caution :  The DIP switches should be set using a pointed implement such as a small screwdriver, a ball-point pen tip or similar. Pencils should not be used because of the risk of graphite particles entering the switch mechanism, and producing short circuits.

Preparing The Host Computer

The computer used for supervising the dataTaker must have a serial interface which supports the RS232 communication standard.

The baud rate of the computer must be set to be the same as that for the dataTaker, and the start bits, stop bits and parity must be set to 8, 1 and None respectively.

If you have a notebook computer which has no RS232 serial interface(s), then you will need a docking module for your particular computer, or a USB to RS232 adaptor, which have an RS232 interface.

The DeTransfer software package supplied with the dataTaker provides for easy communications with the logger. DeTransfer is used to send commands to the dataTaker, and to receive data back from the dataTaker.

A large number of general purpose communications programs can also be used to communicate with the dataTaker.

DeLogger also provides an easy method for supervising the dataTaker, and also has facilities for generating data files, graphs and reports.

Password Protection

The dataTaker has an optional password protection scheme. Whenever a password is defined, no communications are possible until the defined password is entered.

Password protection is most useful when the dataTaker is connected to a modem. The use of a password eliminates the possibility of line noise being interpreted as commands during the establishment of a call.

The Password protection also protects against unauthorized access to the dataTaker.

Using DeTransfer, the password is set by the following general command for example

PASSWORD="password "

Where the password may be any string of up to 10 characters, and is case sensitive.

To establish communications when a password is defined, enter the password followed by a carriage return. This will sign the user on, and communications can proceed until the SIGNOFF command is issued, or if there is no communications activity for 300 seconds (5minutes).

The period before automatic signoff is defined by the Parameter14 command, defines the signoff delay period in seconds (see Section III ñ Parameter Commands). For example the command

P14=15

sets the automatic signoff delay to 15 seconds.

To remove a defined password, firstly establish communications by entering the current password and then enter the command

PASSWORD=""

Page Content


Home

Title and Waranty

Go to: Section 2 | Section 3

Section 1


Construction of the dataTaker 50

Construction of the dataTaker 500 600

Construction of the CEM

Getting Started

 

Section 2


Interfacing

Powering the dataTaker

Powering Sensors from the dataTaker

The Serial Interfaces

The RS232 COMMS Serial Interface

The NETWORK Interface

Analog Process

Connect Analog

Analog Chns

Measuring Low Level Voltages

Measuring High Level Voltages

Measuring Currents

Measuring 4-20mA Current Loops

Measuring Resistance

Measuring Frequency and Period

Measuring Analog Logic State

Measuring Temperature

Measuring Temperature with Thermocouples

Measuring Temperature with RTDs

Measuring Temperature with IC Temperature Sensors

Measuring Temperature with Thermistors

Measuring Bridges and Strain Gauges

Measuring Vibrating Wire Strain Gauges

The Digital Input Channels

Monitoring Digital State

The Low Speed Counters

The Phase Encoder Counter

The High Speed Counters

The Digital Output Channels

The Channel Expansion Module

Installing The Panel Mount Display

 

Section 3


Programming the dataTaker

Communication Protocols and Commands

Entering Commands and Programs

Format of Returned Data

Specifying Channels

The Analog Input Channels

The Digital Input Channels

The Counter Channels

The Digital Output Channels

The Real Time Clock

The Internal Channels

Channel Options

Schedules

Alarms

Scaling Data - Polynomials, Spans and Functions

CVs Calcs and Histogram

Logging Data to Memory

Programming from Memory Cards

STATUS RESET TEST

Switches and Parameters

Networking

Writing Programs

Keypad and Display

Error Mess Text

Appendix A - ASCII

Appendix B - ADC Timing