.MDB File Format in Access Software

.MDB File Format in Access Software

MDB is the default file format used in Microsoft Office Access, up to Access 2003. In the 2007 and 2010 versions, however, Access uses the newer ACCDB file format as the default.

The file extension for the MDB file format is .mdb.

Data, in the context of databases, refers to all the single items that are stored in a database, either individually or as a set. Data in a database is primarily stored in database tables, which are organized into columns that dictate the data types stored therein.

A database (DB), in the most general sense, is an organized collection of data. More specifically, a database is an electronic system that allows data to be easily accessed, manipulated and updated.

In other words, a database is used by an organization as a method of storing, managing and retrieving information. Modern databases are managed using a database management system (DBMS).

Microsoft Office Access is Microsoft’s answer to providing a small database engine. It enables users with little knowledge of database administration to quickly set up their own database. The following versions of Access use the MDB file format as default: Access 95, 97, 2000 and 2003.

In 2007, Microsoft introduced a new file format (the ACCDB file format) with the 2007 version of Access. Access 2010 continues to use the same format. However, the 2007 and 2010 versions are also compatible with the older MDB format.

Earlier Access control Systems manufacturer uses this extension to design Access Management software. Like Syris use cardV3.mdb for master database.

MS Access software allows users to create, manage and query a database using its GUI controls and features, without having to write programming queries.

Access Control in the Retail sector

A guide to Access Control in the Retail sector

What is access control?

Access control provides the ability to control, monitor and restrict the movement of people, assets or vehicles in, out and around a building or site.

Access control is essential in the protection of people and assets and has the additional benefit of being expanded from controlling, for example, a single entrance door to a large integrated security network.

There are also huge potentials in terms of integrating access control with other systems, such as CCTV and intruder alarms, allowing for cost savings and greater security benefits.

What risks does the retail sector face and how can these be countered by access control?

The retail sector faces a variety of threats all year round, including shoplifting, organised retail crime and dishonest staff, and these risks can increase significantly during busy shopping periods such as seasonal sales.

Recently, the BSIA carried out a survey of its members to discover the trends in retail security over the last year. Over 50% of respondents felt that the use of private security measures in retail had increased over the past twelve months, with a further 65% anticipating this use to increase over the course of the next year.

Members perceived the biggest threat to retailers to be shoplifting and petty theft, with theft by employees following in second. Online theft and armed robberies were also considered to be risks.

Retail environments are full of valuable assets, both on the shop floor and in the stock room. Access control systems are all designed to permit access only to people with the necessary authority to enter a particular area, ensuring that goods and people are protected and helping to manage known or anticipated threats.

Generally, systems are comprised of three main components:

1. The physical barrier – to physically restrict access to a building or area. This can be achieved through methods such as:

• Doors – secured by either a magnetic or strike lock, or can be revolving or sliding.

• Turnstiles and speed gates – designed to limit access to one person per identification device.

2. The identification device – there are a number of different technologies available to identify users of an access control system, including:

• A proximity card and reader via Radio-Frequency Identification (RFID) – these cards can be programmed to work at a short or long read range

• A smart card and reader

• A swipe card and reader

• PIN pads

• Biometric devices such as fingerprint or iris scanning

3. The door controller and software – these are at the heart of the access control system and are used to decide who can gain access through which entry point and at what time of the day are they permitted. These can vary depending on the size of the system and how many readers or sites you are trying to control from one point. Some of the options include:

• A stand-alone door controller linked to a single door with no software

• A number of door controllers all linked together to a single PC to control one site

• A number of sites all interlinked together over a wide network area

The added benefits of access control

Retail environments often incorporate large numbers of staff working varied shift patterns. Access control systems can offer a wide range of benefits, including Human Resource management and integrated security systems.

Time and attendance

Retail security does not necessarily just offer protection for the shop floor itself, but can encompass all stages of the supply chain – including staff offices, warehouses and even the delivery process. Naturally, various different employees and outside visitors are involved in these processes and access control systems can assist with staff management.

Badge/token technology can be used to record employee hours and monitor visitor movement within a specific site. If appropriate, these can be processed against working hours, applicable for both temporary and permanent staff – this can be useful for busy shopping periods when additional seasonal staff are employed temporarily. This can work in real time to feed transactions through to the company’s payroll. Time and attendance systems also accurately help keep employers on the right side of the European Working Time regulations and manage holidays and absences effectively. Fast, accurate and easy-to-use, these systems are suitable for businesses employing just a few people, right up to large multinational companies.

Automatic Number Plate Recognition

To monitor the movement of vehicles around an area, CCTV-style cameras and computer software can be used to identify number plates of vehicles. Some systems can also store photographs of the driver and vehicle for subsequent analysis.

This sophisticated software allows critical information to be passed to the police to assist in the pursuit, identification and capture of offenders should an incident occur. For example, if a shoplifter flees the scene of a crime via a vehicle, ANPR cameras situated around an area could help identify the criminal. Visual proof of parking offences with the corresponding time and date information is provided as evidence and to avoid disputes. Using a Driver and Vehicle Licensing Agency (DVLA) link, monitors are then able to identify the owner of a vehicle and process the offence automatically.

Fire roll call

Health and safety is a key consideration for any business. Since retail environments involve multiple staff members with varying shift patterns, it can be difficult to keep track of all employees during an emergency. Fire roll call technology generates a report containing crucial information in relation to who is within the building and potentially where they are. This software operates via the access control smart card or fob that an employee uses to gain access to or exit a building. In the event of an emergency, the fire roll-call software alerts occupants to the emergency whilst simultaneously activating the report at a safe pre-determined remote point.

Please note: In order for the fire roll call software to effectively carry out its function, employees and visitors must always present their card or badge. The use of smart card or RFID controlled turnstiles can help in this situation.

Integrated security systems

For maximum security, retail environments can benefit from a fully integrated access control system with CCTV, intruder alarms, fire detection and building management systems. One way to attain this is by adopting the use of Internet Protocol (IP) technology, which allows these systems to communicate with each other to maximise their effectiveness.

Separate access control and intruder alarm systems, for example, could allow an employee to access an area that is set with an alarm.

However, unless the employee has the authority to unset the system, the access would result in a false alarm being activated – potentially causing panic in a retail environment. An effectively integrated system would recognise that the user does not have the authority to unset the system, so would not allow them in the area to begin with.

What else should you know when considering access control?

An initial risk assessment of an area can determine the level of security required and subsequently influence the access control system you choose. BSIA access control members and professional security consultancies can assist with this.

BSIA members are subject to rigorous checks before they are admitted into membership, meaning that you are selecting a quality company. Below are just some of the reasons why BSIA members can offer you peace of mind:

• They are independently inspected to the quality standard ISO 9001 with a UKAS accredited inspectorate

• They comply with relevant British and European Standards and codes of practice

• Are financially sound

• Professional

• Staff vetting has been conducted where necessary

• They are technically proficient and committed to quality training and development

• They are up-to-date with the latest developments in British and European policy and legislation

What legislation should you be aware of?

The Disability Discrimination Act was amended in 2005 and has a significant impact not only in terms of the design of new systems, but also means that many systems may need to be upgraded to ensure compliance and adequate, user friendly access to the building for all staff and visitors.

Other considerations to be aware of:

National minimum care standards

Health and Safety at Work Act

Occupiers Liability Act
Management of Health and Safety at Work Regulations.

What happens during a fingerprints scan

What happens during a fingerprints scan?

What is a Fingerprint?

The skin surface of the fingers, palms and soles of the feet is different to the rest of the body surface. If you look at the inner surface of your hands and soles of the feet you will see a series of lines made up of elevations which we call 'ridges' and depressions which we call 'furrows'.

These ridges and furrows can be recorded in many ways. For example, the ridges can be inked and placed on to a piece of paper. This would leave a fingerprint like below. The black lines represent the ridges and the white lines represent the furrows.

Within these patterns the ridges can split or end creating ridge characteristics. There are 6 types of ridge characteristics.

Everyone has a unique and different distribution of these characteristics that develop in the womb and are persistent throughout life.

It is the coincidence sequence of these characteristics that allow me to make identifications. The coincidence sequence is whereby I will find the same characteristics, in the same order with the same relationship to each other in both the crime scene fingerprint and the fingerprint on the form I am using.

Fingerprints unique:

It's pretty obvious why we have fingerprints—the tiny friction ridges on the ends of our fingers and thumbs make it easier to grip things. By making our fingers rougher, these ridges increase the force of friction between our hands and the objects we hold, making it harder to drop things. You have fingerprints even before you're born. In fact, fingerprints are completely formed by the time you're seven months old in the womb. Unless you have accidents with your hands, your fingerprints remain the same throughout your life.

Enrollment and verification

Suppose you're in charge of security for a large bank and you want to put a fingerprint scanning system on the main entry turnstile where your employees come in each morning. How exactly would it work?

There are two separate stages involved in using a system like this. First you have to go through a process called enrollment, where the system learns about all the people it will have to recognize each day. During enrollment, each person's fingerprints are scanned, analyzed, and then stored in a coded form on a secure database. Typically it takes less than a half second to store a person's prints and the system works for over 99% of typical users (the failure rate is higher for manual workers than for office workers).

Once enrollment is complete, the system is ready to use—and this is the second stage, known as verification. Anyone who wants to gain access has to put their finger on a scanner. The scanner takes their fingerprint, checks it against all the prints in the database stored during enrollment, and decides whether the person is entitled to gain access or not. Sophisticated fingerprint systems can verify and match up to 40,000 prints per second!

How fingerprint scanners work

a computer has to scan the surface of your finger very quickly and then turn the scanned representation into a code it can check against its database. How does this happen?

There are two main ways of scanning fingers. An optical scanner works by shining a bright light over your fingerprint and taking what is effectively a digital photograph. If you've ever photocopied your hand, you'll know exactly how this works. Instead of producing a dirty black photocopy, the image feeds into a computer scanner. The scanner uses a light-sensitive microchip (either a CCD, charge-coupled device, or a CMOS image sensor) to produce a digital image. The computer analyzes the image automatically, selecting just the fingerprint, and then uses sophisticated pattern-matching software to turn it into a code.

Another type of scanner, known as a capacitive scanner, measures your finger electrically. When your finger rests on a surface, the ridges in your fingerprints touch the surface while the hollows between the ridges stand slightly clear of it. In other words, there are varying distances between each part of your finger and the surface below. A capacitive scanner builds up a picture of your fingerprint by measuring these distances. Scanners like this are a bit like the touchscreens on things like iPhones and iPads.

Unlike ordinary digital photos, scans have to capture exactly the right amount of detail—brightness and contrast—so that the individual ridges and other details in the fingerprint can be accurately matched to scans taken previously. Remember that fingerprints might be used as evidence in criminal trials, where a conviction could result in a long jail sentence or even the death penalty. That's why "quality control" is such an important part of the fingerprint scanning process.

Here's how the process works with a simple optical scanner:

1.    A row of LEDs scans bright light onto the glass (or plastic) surface on which your finger is pressing (sometimes called the platen).

2.    The quality of the image will vary according to how you're pressing, how clean or greasy your fingers are, how clean the scanning surface is, the light level in the room, and so on.

3.    Reflected light bounces back from your finger, through the glass, onto a CCD or CMOS image sensor.

4.    The longer this image-capture process takes, the brighter the image formed on the image sensor.

5.    If the image is too bright, areas of the fingerprint (including important details) may be washed out completely—like an indoor digital photo where the flash is too close or too bright. If it's too dark, the whole image will look black and details will be invisible for the opposite reason.

6.    An algorithm tests whether the image is too light or too dark; if so, an audible beep or LED indicator alerts the operator and we go back to step 1 to try again.

7.    If the image is roughly acceptable, another algorithm tests the level of detail, typically by counting the number of ridges and making sure there are alternate light and dark areas (as you'd expect to find in a decent fingerprint image). If the image fails this test, we go back to step 1 and try again.

8.    Providing the image passes these two tests, the scanner signals that the image is OK to the operator (again, either by beeping or with a different LED indicator). The image is stored as an acceptable scan in flash memory, ready to be transmitted (by USB cable, wireless, Bluetooth, or some similar method) to a "host" computer where it can be processed further. Typically, images captured this way are 512×512 pixels (the dimensions used by the FBI), and the standard image is 2.5cm (1 inch) square, 500 dots per inch, and 256 shades of gray.

9.    The host computer can either store the image on a database (temporarily or indefinitely) or automatically compare it against one or many other fingerprints to find a match.

The matching algorithm finds out whether there is a match by comparing two templates extracted by the characteristic point extraction algorithm, specifically by comparing the positions of each characteristic point and the structure.

Attendance System based on Biometrics

Attendance System based on Biometrics

If you are still using paper and calculator to prepare the salary of the employees then you are wasting your valuable time and missing the benefits of biometric attendance systems. In this era of modern technology, monitoring attendance of each employee to payroll activity has become seamless.

What is Biometrics Technology?

The Biometrics technologies used to measure and analyze personal characteristics, both physiological and behavioral. These characteristics include fingerprints, voice patterns, hand measurements, irises and others, all used to identify human characteristics and to verify identity. These biometrics or characteristics are tightly connected to an individual and cannot be forgotten, shared, stolen or easily hacked. These characteristics can uniquely identify a person, replacing or supplementing traditional security methods by providing two major improvements: personal biometrics cannot be easily stolen and an individual does not need to memorize passwords or codes. Since biometrics can better solve the problems of access control, fraud and theft, more and more organizations are considering biometrics a solution to their security problems. Biometrics gives you an alternative and higher security compared to passwords or pin identification due to the fact that passwords and pin #s can easily be compromised.

Authentication by biometric verification is becoming increasingly common in corporate and public security systems, consumer electronics and point of sale (POS) applications. In addition to security, the driving force behind biometric verification has been convenience. Biometric devices, such as fingerscanners, consist of:

Ø A reader or scanning device

Ø Software that converts the scanned information into digital form and compares match points

Ø A database that stores the biometric data for comparison

To prevent identity theft, biometric data is usually encrypted when it's gathered. Here's how biometric verification works on the back end: To convert the biometric input, a software application is used to identify specific points of data as match points. The match points in the database are processed using an algorithm that translates that information into a numeric value. The database value is compared with the biometric input the end user has entered into the scanner and authentication is either approved or denied.

What is Biometric Attendance System?

Biometric time attendance system used to track each and every person coming to your place is actually who he claims to be or not with its time and other details. It uses finger and face recognition system to verify person's identity and record its time-in and time-out with all required details.

Benefits of Biometric System

Ø It has many advantages over conventional time tracking used at organizations. Typically such organizations maintain a register book, where people entry their name, time-in, time-out and other required details but the problem with this manual system is inaccuracy, time consuming, unreliable and most important is less secure.

Ø Biometric time attendance is very user friendly and easy to use; any person can use it very easily. It is very fast also, user has to see once in front of system and all details including its time will be recorded automatically. In this way it saves lot of time and still record details very accurately. One can avoid early punching, late punching and buddy punching very easily.

Ø Many schools, college used Biometric Time Attendance to track their student's attendance. The Biggest advantage of Biometric Time Attendance over manual tracking is better security. Many shops and shopping mall use biometric time attendance for security purpose and it really works a lot.

Ø If someone wants to use it for business or organization, then they can easily integrate it to payroll systems, account systems and billing systems. So in that way it is very flexible also and it also shows that time attendance system can be used for all type of business and organizations with great flexibility.

Ø In a nutshell biometric time attendance solution permits you to focus on your core business by giving quickest and easiest way to overcome your time tracking issues.

Return on Investment in Biometric System Installations..

Biometric time clocks, which are used to record employee start and end times, are popular in organizations where security is an issue, or where employees may falsely record their time worked. Because biometric technology is more expensive than other forms of time clock identification, such as magnetic badges or personal identification numbers, it is important to evaluate the potential return on investment should biometric devices be installed. In service environments where employees punch in and out to work, return on investment can be considerable because biometric devices virtually eliminate the ability of employees to “buddy punch.” 

In buddy punching, an employee either types a tardy employee’s PIN or swipes the tardy employee’s badge earlier than he arrives to work or after he leaves work. The organizational costs of this kind of time theft can be enormous. The company loses money a few minutes at a time compounded across departments and locations. Biometrics makes it almost impossible for employees to defraud a time and attendance system. 

Other returns on investment can be gained through the use of the biometric system as a security access monitor, as well. In this case, the biometric system is used to grant or deny access to restricted areas. The cost of purchasing and maintaining magnetic or proximity identification cards, which do not prevent fraudulent access, can be eliminated.

You need an Access Control Systems

Do you need an Access Control Systems?

Access control security systems are designed to restrict physical entry to only users with authorization. Many organizations, governmental and private, have started adopting access control security systems for physical entry into their facilities. Whether it is a simple non intelligent access control system like a punching in a password, or advanced biometric systems that scan and permit entry very specifically, there are many advantages to employing these security systems.
It is important for businesses of every size to keep important data and remove threats. All businesses acknowledge this basic security concern by placing locks on the door and giving keys to employees that need to access these locks. If you answer yes to any of the following questions, you may need access control systems:

• • Is a lost or stolen key a security threat to your business?
  • Time Based Control for Security Systems
  • Do you need different access for different employees and clients?
  • Would it be really beneficial to restrict access based on time or day?
  • Do you need a record of people’s “comings and goings?
  • Could your employees/clients be more secure?
  • Reduced Requirement for Manpower
  • Biometric Systems

Benefits of access control systems

The benefits of access control systems are thus many:

• Audit trail – With access control systems, you will have a record of every opening and attempted opening of each door or specific area. The audit trail can be valuable in resolving employee issues.
• Time/day restrictions – Do you have certain employees that should only be there at certain times and days. An access control system make more sense to control their access than to give them a key that allows access at any time or day.
• Lost or stolen keys – When keys are lost or stolen, it is an expensive process for a business to completely rekey each door. Access control systems allow you to remove access by deactivating the I.D. badges or other security credentials.
• Remote access control – Many access control systems allow you to control of all of the business’ locks from one main system. With access control systems, you can easily and quickly lock down your businesses in an emergency as well as add and remove credentials.

Design 1:

Design 2: Single Door

Design 3: 4-Door single controller.

Design 4: New Concept, PoE Based

Design 5: SYRiS Product with SQL Database, Multi-location. One SY230NT Controller can controll 4nos of Door. Practically i do many projects with this.

How the Access Control System WorksØ  The typical access control system consists of a card/ pin reader, electromagnetic lock or door strike, power supply system and a push button.
Ø  The valid and authorized card user must present the card to the security system.
Ø  Upon verification by the reader, the locking system will be de-energized and the door can be pushed open.
Ø  To exit the premises, the person will have to press a door lock release switch and the system will release the lock.
Ø  A power back up is also installed while fitting in the access control system.
Ø  A break glass is also incorporated in case of emergency.

RS-232 cable Wiring & Testing

COM Port (OR) RS-232 cable Wiring & Testing

As A technical background eSecurity Professional, many time got call “my Access Controller communication has RS232 enable How we connect with Computer (COM Port), is there any layout” Sometime “Successfully testing via my Laptop but Customer computer not responding, any distance or new programming is there”. I remember in year 2006 me also facing this type of problem with an Access Controller; I would be like to share the myth.

Com Port (Com1 / Com2 etc)= Serial Port = RS232 = Consol.

The wiring of RS232 has always been a problem. Originally the standard was defined for DTE (data terminal equipment) to DCE (data communication equipment connection), but soon people started to use the communication interface to connect two DTEs directly using null modem cables. No standard was defined for null modem connections with RS232 and not long after their introduction, several different wiring schemes became common. With Digital Equipment Corporation tried to define their own standard for serial interconnection of computer devices with modified modular jack connectors. This interfacing standard became available on most of their hardware, but it wasn't adopted by other computer manufacturers. Maybe because DEC used an non-standard version of the modular jack.

Very interesting is the RS232 to RJ45 wiring standard proposed by Dave Yost in 1987, based on earlier wiring schemes used at Berkeley University. He tried to define a standard comparable to DEC, where both DTEs and DCEs could be connected with one cable type. This standard was published in the Unix System Administration Handbook in 1994, and has since that moment been a wiring standard for many organizations. We will discuss this standard in detail here.

The RS-232 standard 9600bps port will drive 13 metres of shielded cable. RS232 standard is an asynchronous serial communication method. The word serial means, that the information is sent one bit at a time. Asynchronous tells us that the information is not sent in predefined time slots. RS232 sending of a data word can start on each moment. If starting at each moment is possible, this can pose some problems for the receiver to know which is the first bit to receive. To overcome this problem, each data word is started with an attention bit. This attention bit, also known as the start bit, is always identified by the space line level. Directly following the start bit, the data bits are sent. Data bits are sent with a predefined frequency, the baud rate. Both the transmitter and receiver must be programmed to use the same bit frequency. After the first bit is received, the receiver calculates at which moments the other data bits will be received. It will check the line voltage levels at those moments. With RS232, the line voltage level can have two states. The on state is also known as mark, the off state as space. No other line states are possible. When the line is idle, it is kept in the mark state. For error detecting purposes, it is possible to add an extra bit to the data word automatically. The transmitter calculates the value of the bit depending on the information sent. The receiver performs the same calculation and checks if the actual parity bit value corresponds to the calculated value. The stop bit identifying the end of a data frame can have different lengths. Actually, it is not a real bit but a minimum period of time the line must be idle (mark state) at the end of each word. On PC's this period can have three lengths: the time equal to 1, 1.5 or 2 bits. 1.5 bits is only used with data words of 5 bits length and 2 only for longer words. A stop bit length of 1 bit is possible for all data word sizes.

Goals of the Yost device wiring standard

The mess with RS232 wiring is widely known. It was the reason for starting this website. Dave Yost wanted to solve that mess once and for all, reaching as much as possible of the following goals:

1. All cable connectors should have the same connector type (RJ45)
2. All cable connectors should have the same connector gender (male)
3. DTEs and DCEs should have the same connector wiring
4. All cables should be identical (except for length)
5. No need for null modems or other special cables for specific situations

These goals are very close to the goals DEC wanted to achieve. The Yost standard has however one basic advantage. Because RJ45 connectors are used, eight pins are available which makes it possible to transfer almost all RS232 signals. Therefore the Yost standard can be used with much more equipment.

Yost DTE adapter wiring

Now we know how the cables are wired, it is time to define the adapter wiring for various equipment. Depending of the type of equipment, DB9 or DB25 connectors are used. Layouts for both connectors to a RJ45 socket for DTE equipment is shown here. The colors are defined by the Yost standard. The DTR to DSR connection is optional. Please use the manual of the device or software to decide if this loop is necessary. It doesn't harm most of the time if you connect both lines, even with systems that don't use the DSR input signal.

Test COM port by using HyperTerminal.

The HyperTerminal application has been distributed with the Windows operating system versions for a long time now, and for administrators and technical support Representatives, it can be a very useful tool. HyperTerminal allows a user to make a connection to a "host" system from a Windows computer using an available COM port. This will enable you to verify whether or not a port is active and open.  If you have never looked at HyperTerminal, take a couple of minutes to read through the following and see how it can make your life easier.

The HyperTerminal application is started by default from the Start | Programs | Accessories | Communications | HyperTerminal location. When you start HyperTerminal, you are asked to name the connection you are about to configure. This is useful as once you have configured your connection, you can then save all the settings to a configuration file of the same name. This configuration file can be used to implement equivalent settings for subsequent connections. After selecting a connection name, click OK.

On the Connect To dialog box, you are introduced to the different types of connection that HyperTerminal offers. By default, a dial-up connection using a modem is selected (assuming you have a modem present). If you have installed an external modem in addition to an internal modem that modem should also be present in the drop down menu as a choice.

 If you click the downwards arrow on the Connect Using field, you may see one or more COMx (where x is the number of the COM port. i.e COM5) options depending on the number of serial ports available on your computer. The COMx options are typically used for attaching to something like a UNIX computer via serial cable or to a router via its serial console cable. 

To test a specific COM port select that COM port you wish to test. Once the COM port is selected you will not be able to access the other options on this dialog box. They will appear grayed out.

Click OK and select these options:

9600 Bits Per Second, 8 Data Bits, No Parity, 1 Stop Bit, and Hardware Flow Control.

Before clicking OK on the COM3 Properties Dialog Box look at the lower left corner of the HyperTerminal Window. Notice it says "Disconnected" See graphic Below.

Now click the OK button on the COM3 Properties Dialog box. Watch the lower left corner of the HyperTerminal Windows. If the COM port is available and can be opened you will see the status change to Connected. See graphic below.

 If you select OK and get an error saying "Unable to open COMx (where x is the COM port number). Please check your port settings". The COM port you are testing is being used by some device or is not functioning correctly.

Start at the beginning of the COM port test and test another available COM port.

If you receive the error we discussed on every port you select then there are no available ports and you will need to either troubleshoot further or speak to your hardware manufacturer and ask your manufacturer to recommend a hardware solution appropriate for your situations.

Test COM port by using Loopback tester

This is a simple and useful tool for testing RS-232 ports in DTE equipment are working working or not. This plug is connected so that every sent character is echoed back.

 If you Short DB9 (Com Port / RS232) Pin 2 & 3, & Press any Word via Keypad, you can get Eco of that Key. IF you got replied then your Com port is Working Normal, IF not then need to either troubleshoot further or speak to your hardware manufacturer and ask your manufacturer to recommend a hardware solution appropriate for your situations.

Differences between RS-232 and full-duplex RS-485

From a software point of view, full-duplex RS-485 looks very similar to RS-232. With 2 pairs of wires -- a dedicated "transmit" pair and a dedicated "receive" pair (similar to some Ethernet hardware), software can't tell the difference between RS-485 and RS-232.

From a hardware point of view, full-duplex RS-485 has some major advantages over RS-232 -- it can communicate over much longer distances at higher speeds.

Alas, a long 3-conductor cable intended for RS-232 cannot be switched to full-duplex RS-485, which requires 5 conductors.

RS-232 is only defined for point-to-point connections, so you need a separate cable for each sensor connected to a host CPU. RS-485 allows a host CPU to talk to a bunch of sensors all connected to the same cable.

Differences between RS-232 and half-duplex RS-485

But a lot of RS-485 hardware uses only 1 pair of wires (half-duplex). In that case, the major differences are

• Each RS-485 node, including the host CPU, must "turn off the transmitter" when done transmitting a message, to allow other devices their turn using the shared medium
• The RS-485 hardware generally receives on the receiver every byte that was transmitted by every device on the shared medium, including the local transmitter. So software should ignore messages sent by itself.

A long 3-conductor cable intended for RS-232 can often be switched to half-duplex RS-485, allowing communication at higher speeds and at higher external noise levels than the same cable used with RS-232 signaling.

RS-232 is only defined for point-to-point connections, so you need a separate cable for each sensor connected to a host CPU. RS-485 allows a host CPU to talk to a bunch of sensors all connected to the same cable.

Alas, half-duplex RS-485 networks are often more difficult to debug when things go wrong than RS-232 networks, because

• When a "bad message" shows up on the cable, it is more difficult (but not impossible) to figure out which node(s) transmitted that message when you have a shared-medium with a dozen nodes connected to the same single cable, compared to a point-to-point medium with only 2 nodes connected to any particular cable.
• Transmitting data bidirectionally over the same wire(s), rather than unidirectional transmission, requires a turn-around delay. The turn-around delay should be proportional to the baud rate -- too much or too little turn-around delay may cause timing problems that are difficult to debug.

Differences between RS-232 and both kinds of RS-485

RS-485 signal levels are typically 0 to +5 V relative to the signal ground.

RS-232 signal levels are typically -12 V to +12 V relative to the signal ground.

RS-232 uses point-to-point unidirectional signal wires: There are only two devices connected to a RS-232 cable. The TX output of a first device connected to the RX input of a second device, and the TX output of the second device connected to the RX input of the first device. In a RS-232 cable, data always flows in only one direction on any particular wire, from TX to RX.

RS-485 typically uses a linear network with bidirectional signal wires: There are typically many devices along a RS-485 shared cable. The "A" output of each device is connected to the "A" output of every other device. In a RS-485 cable, data typically flows in both directions along any particular wire, sometimes from the "A" of the first device to the "A" of the second device, and at a later time from the "A" of the second device to the "A" of the first device.