Differential Manchester Encoding (DM) is a line code in which data and clock signals are combined to form a single 2-level self-synchronizing data stream. In various specific applications, this line code is also called by various other names, including Biphase Mark Code (CC), Frequency Modulation (FM), F2F (frequency/double frequency), Aiken Biphase, and Conditioned diphase.
DM is a differential encoding, using the presence or absence of transitions to indicate logical value. It is not necessary to know the polarity of the sent signal since the information is not represented by the absolute voltage levels but in their changes: in other words it does not matter which of the two voltage levels is received, but only whether it is the same or different from the previous one; this makes synchronization easier.
Differential Manchester encoding has the following advantages over some other line codes:
A transition is guaranteed at least once every bit, for robust clock recovery.
In a noisy environment, detecting transitions is less error-prone than comparing signal levels against a threshold.
Unlike with Manchester encoding, only the presence of a transition is important, not the polarity. Differential coding schemes will work exactly the same if the signal is inverted (e.g. wires swapped). Other line codes with this property include NRZI, bipolar encoding, coded mark inversion, and MLT-3 encoding.
If the high and low signal levels have the same magnitude with opposite polarity, the average voltage around each unconditional transition is zero. Zero DC bias reduces the necessary transmitting power, minimizes the amount of electromagnetic noise produced by the transmission line, and eases the use of isolating transformers.
These positive features are achieved at the expense of doubling the bandwidth—there are two clock ticks per bit period (marked with full and dotted lines in the figure). At every second clock tick, marked with a dotted line, there is a potential level transition conditional on the data. At the other ticks, the line state changes unconditionally to ease clock recovery. One version of the code makes a transition for 0 and no transition for 1; the other makes a transition for 1 and no transition for 0.
Differential Manchester is specified in the IEEE 802.5 standard for token ring LANs, and is used for many other applications, including magnetic and optical storage. As Biphase Mark Code (BMC), it is used in AES3, S/PDIF, SMPTE time code, and USB PD. Many magnetic stripe cards also use BMC encoding, often called F2F (frequency/double frequency) or Aiken Biphase, according to the ISO/IEC 7811 standard. Differential Manchester is also the original "frequency modulation" (FM) used on "single-density" floppy disks, followed by "double-density" modified frequency modulation (MFM), which gets its name from its relation to FM, or Differential Manchester, encoding.ISO/IEC 4909
ISO/IEC 4909:2006 establishes specifications for financial transaction cards using track 3 and is intended to permit interchange based on the use of magnetic stripe encoded information. It specifies the data content and physical location of read/write information on track 3 and is to be used in conjunction with the relevant parts of ISO/IEC 7811 and ISO/IEC 7812.
ISO/IEC 4909:2006 recognizes the need for formats of track 3 which can be used independently of, or in conjunction with, track 2 as defined in ISO/IEC 7813. This approach is intended to permit the greatest degree of flexibility within the financial community in facilitating international interchange.
Using track 3 in conjunction with track 2 is a mode of operation in both on-line and off-line interchange environments. This mode of operation requires that the original encoded data on track 2 be read; the data on track 3 be read; and, if update is required, all the data on track 3 be rewritten.
Independent use of track 3 is an alternative mode of operation permitting both on-line interchange and off-line interchange based on mutual agreement between interested parties. It requires reading only of the data on track 3 and, if update is required, the rewriting of all the data on track 3.ISO/IEC 7810
ISO/IEC 7810 Identification cards — Physical characteristics is an international standard that defines the physical characteristics for identification cards.The characteristics specified include:
Resistance to bending, flame, chemicals, temperature, and humidity
ToxicityThe standard includes test methods for resistance to heat.ISO/IEC 7813
ISO/IEC 7813 is an international standard codified by the International Organization for Standardization and International Electrotechnical Commission that defines properties of financial transaction cards, such as ATM or credit cards.ISO/IEC JTC 1/SC 17/WG 1
ISO/IEC JTC 1/SC 17/WG 1 is a working group within ISO/IEC JTC1 of the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC), that facilitates standards development within the field of cards and personal identification. A national delegation of experts from various countries meet in person at WG1 to discuss and debate items detailed in a meeting agenda until a consensus is reached. These items include: draft standards, draft test methods, questions from the industry, proposals for new work items or other aspects relating to the Standards and Test Methods that WG1 bears responsibility for. WG1 meetings are usually held three times a year, typically at the beginning of March, the end of June, and at the beginning of October for a period of 2–3 days. The October meeting is typically held in the days just prior to the SC17 Plenary and at the same location.List of International Organization for Standardization standards, 5000-7999
This is a list of published International Organization for Standardization (ISO) standards and other deliverables. For a complete and up-to-date list of all the ISO standards, see the ISO catalogue.The standards are protected by copyright and most of them must be purchased. However, about 300 of the standards produced by ISO and IEC's Joint Technical Committee 1 (JTC1) have been made freely and publicly available.Magnetic stripe card
A magnetic stripe card is a type of card capable of storing data by modifying the magnetism of tiny iron-based magnetic particles on a band of magnetic material on the card. The magnetic stripe, sometimes called swipe card or magstripe, is read by swiping past a magnetic reading head. Magnetic stripe cards are commonly used in credit cards, identity cards, and transportation tickets. They may also contain an RFID tag, a transponder device and/or a microchip mostly used for business premises access control or electronic payment.
Magnetic recording on steel tape and wire was invented in Denmark around 1900 for recording audio. In the 1950s, magnetic recording of digital computer data on plastic tape coated with iron oxide was invented. In 1960, IBM used the magnetic tape idea to develop a reliable way of securing magnetic stripes to plastic cards, under a contract with the US government for a security system. A number of International Organization for Standardization standards, ISO/IEC 7810, ISO/IEC 7811, ISO/IEC 7812, ISO/IEC 7813, ISO 8583, and ISO/IEC 4909, now define the physical properties of the card, including size, flexibility, location of the magstripe, magnetic characteristics, and data formats. They also provide the standards for financial cards, including the allocation of card number ranges to different card issuing institutions.Payment card
Payment cards are part of a payment system issued by financial institutions, such as a bank, to a customer that enables its owner (the cardholder) to access the funds in the customer's designated bank accounts, or through a credit account and make payments by electronic funds transfer and access automated teller machines (ATMs). Such cards are known by a variety of names including bank cards, ATM cards, MAC (money access cards), client cards, key cards or cash cards.
There are a number of types of payment cards, the most common being credit cards and debit cards. Most commonly, a payment card is electronically linked to an account or accounts belonging to the cardholder. These accounts may be deposit accounts or loan or credit accounts, and the card is a means of authenticating the cardholder. However, stored-value cards store money on the card itself and are not necessarily linked to an account at a financial institution.
It can also be a smart card that contains a unique card number and some security information such as an expiration date or CVVC (CVV) or with a magnetic strip on the back enabling various machines to read and access information. Depending on the issuing bank and the preferences of the client, this may allow the card to be used as an ATM card, enabling transactions at automatic teller machines; or as a debit card, linked to the client's bank account and able to be used for making purchases at the point of sale; or as a credit card attached to a revolving credit line supplied by the bank.
Most payment cards, such as debit and credit cards can also function as ATM cards, although ATM-only cards are also available. Charge and proprietary cards cannot be used as ATM cards. The use of a credit card to withdraw cash at an ATM is treated differently to a POS transaction, usually attracting interest charges from the date of the cash withdrawal. Interbank networks allow the use of ATM cards at ATMs of private operators and financial institutions other than those of the institution that issued the cards.
All ATM machines, at a minimum, will permit cash withdrawals of customers of the machine's owner (if a bank-operated machine) and for cards that are affiliated with any ATM network the machine is also affiliated. They will report the amount of the withdrawal and any fees charged by the machine on the receipt. Most banks and credit unions will permit routine account-related banking transactions at the bank's own ATM, including deposits, checking the balance of an account, and transferring money between accounts. Some may provide additional services, such as selling postage stamps.
For other types of transactions through telephone or online banking, this may be performed with an ATM card without in-person authentication. This includes account balance inquiries, electronic bill payments, or in some cases, online purchases (see Interac Online).
ATM cards can also be used on improvised ATMs such as "mini ATMs", merchants' card terminals that deliver ATM features without any cash drawer. These terminals can also be used as cashless scrip ATMs by cashing the receipts they issue at the merchant's point of sale.Six-bit character code
A six-bit character code is a character encoding designed for use on computers with word lengths a multiple of 6. Six bits can only encode 64 distinct characters, so these codes generally include only the upper-case letters, the numerals, some punctuation characters, and sometimes control characters. Such codes with additional parity bit were a natural way of storing data on 7-track magnetic tape.
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