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Frequently Asked Questions

1What is reader collision?

One problem encountered with RFID is the signal from one reader can interfere with the signal from another where coverage overlaps. This is called reader collision. One way to avoid the problem is to use a technique called time division multiple access, or TDMA. In simple terms, the readers are instructed to read at different times, rather than both trying to read at the same time. This ensures that they don't interfere with each other. But it means any RFID tag in an area where two readers overlap will be read twice. So the system has to be set up so that if one reader reads a tag another reader does not read it again. 

2How to perform SAM encryption on MIFARE® DESFire® EV1 card?

 Supporting MIFARE®  DESFire® EV1 technology with the Advanced Encryption Standard (AES), the reader uses an embedded SAM (Secure Access Module) for cryptographic operations, equipped with hardware security measures that allow the safe and secure storage of secret keys. In a typical application, the SAM is used to authenticate the MIFARE® DESFire® EV1 card and decrypt data read from the card using the AES cryptographic standard with 128-bit keys. The embedded SAM is environmentally secure from weather and can be upgraded through application or configuration cards.

3What is NFC?

Near Field Communication (NFC) is a short-range wireless connectivity technology standard designed for intuitive, simple and safe communication between electronic devices. Since NFC complements the existing ISO/IEC 14443 standard for contactless technology, NFC can be compatible with existing contactless card infrastructures.

Extending the ability of contactless technology, NFC enables devices to share information through a distance less than 4 cm, with a maximum communication speed of 424~848 kbps. 

4What are the advantages of NFC (near field communication) comparing with Bluetooth technology?

Most smartphones users have connected to another smartphone or device, such as a wireless headset, using Bluetooth before, or have at least heard of the concept. Bluetooth can connect to devices up to 32 feet way, yet NFC can connect to devices at a maximum distance of 4 centimeters on average. Why is NFC so exciting if it is so limited in range?

Unlike Bluetooth, NFC can interact with another device with a single wave of your smartphone. It’s fast and requires little effort on your part. In contrast, Bluetooth connections take time and require many steps to active. With such a close range between devices required, the potential for signal interference or hackers trying to steal your data is reduces.


Finally, Bluetooth consumes a chunk of your smartphone’s power while NFC typically consumes much less. In cases where your phone is powering another device this isn’t the case, but in other situations you can connect quickly and with minimal power requirements using NFC.

Best of all, if you really need to establish a constant connection and you don’t wait to spend an hour standing nose-to-nose with your coworker, NFC can connect your smartphones before turning the signal over to another technology, such as Bluetooth, giving you the best of both world in terms of speed and distance.

5What is the difference between low-, high-, and ultra-high frequencies?

Just as your radio tunes in to different frequency to hear different channels, RFID tags and readers have to be tuned to the same frequency to communicate. RFID systems use many different frequencies, but generally the most common are low- (around 125 KHz), high- (13.56 MHz) and ultra-high frequency, or UHF (850-900 MHz). Microwave (2.45 GHz) is also used in some applications. Radio waves behave differently at different frequency, so you have to choose the right frequency for the right application.

Now Civintec devices focus on HF 13.56MHz and LF EM125KHz technology.

6What’s the communication distance for serial port transmitting?


The standard does not define a maximum cable length but instead defines the maximum capacitance that a compliant drive circuit must tolerate. A widely used rule of thumb indicates that cables more than 50 feet (15 m) long will have too much capacitance, unless special cables are used. By using low-capacitance cables, full speed communication can be maintained over larger distances up to about 1,000 feet (300 m). For longer distances, other signal standards are better suited to maintain high speed.


RS-485 enables the configuration of inexpensive local networks and multidrop communications links. It offers data transmission speeds of 35 Mbit/s up to 10 m and 100 kbit/s at 1200 m. Since it uses a differential balanced line over twisted pair (like RS-422), it can span relatively large distances (up to 4,000 feet (1,200 m)). A rule of thumb is that the speed in bit/s multiplied by the length in meters should not exceed 108. Thus a 50 meter cable should not signal faster than 2 Mbit/s.

7What is the difference between active and passive technology?

Active RFID tags have a battery, which is used to run the microchip's circuitry and to broadcast a signal to a reader (the way a cell phone transmits signals to a base station). Passive tags have no battery. Instead, they draw power from the reader, which sends out electromagnetic waves that induce a current in the tag's antenna. Semi-passive tags use a battery to run the chip's circuitry, but communicate by drawing power from the reader.

8What is the anti-passing back function?

The anti-passing backfeature is designed to prevent misuse of the access control system. The anti-passing back feature establishes a specific sequence in which access cards must be used in order for the system to grant access.

It is most commonly used at parking gates, where there is both an “in” reader at the entry gate and an “out” reader at the exit gate. This feature requires that for every use of a card at the “in” reader,
there be a corresponding use at the “out” reader before the card can be used at the “in” reader again.

For the typical user of the parking lot, this works fine, because the user would normally swipe their card at the “in” reader to get into the lot in the morning, and swipe it at the “out” reader to get out of the lot in the evening. So long as the sequence is “in – out – in – out – in – out”, everything works fine. However, if a user swipes his card at the “in” reader to get in, and then passes his card back to a friend, the card would not work the second time when it was swiped by the friend. The attempt to use the card a second time would create an “in – in” sequence that is a violation of the anti-passing back rules, and this is why access would be denied.

Anti-passing back can also be used at employee entrance doors. This requires that a card reader be installed on both the inside and the outside of the door. Employees are required to both "card-in" when they enter the building and "card-out" when they leave the building. The anti-passing back feature is also commonly used with turnstiles.

9 What is the difference between MIFARE plus® S and plus X technology?

PLUS S has no secure level2, that means in Intializing, has no 9002 key ; PLUS S only support Plain+CMAC data transmit no cypering commands ; PLUS X has all functionality.