Cash register interface ZVT: National communication standard between terminal and cash register software?

19 February 2021

Cashless payments at POS require a cash register and a payment terminal (also called POS terminal or payment terminal). That much is clear. But in order to manage payments as fast, smooth and safe as possible, cash register and payment terminal also need to be able to communicate. For this, communication protocols such as the ZVT protocol must be integrated as cash register interfaces into the respective cash register software.

But which cash register interfaces are there? What exactly is the ZVT interface and why is it so important? What are the benefits of this communication protocol compared to other cash register interfaces? Where can I find the exact specifications of the interface? And what do cash register interfaces have to do with independence and flexibility? treibauf will shed light on the integration of POS terminals.

Content of the article

    What’s the purpose of cash register interfaces?

    In general, POS terminals can be used autonomously, i.e. without communicating with the POS software. Autonomous use is, however, very time-consuming and susceptible to mistakes.

    The amount from the cash register needs to be manually typed into the terminal, number for number. This obviously not only takes time with each payment, copying over by hand also makes each payment susceptible to human error.

    Integrated use of the POS terminal

    In contrast, there is the integrated use of the POS terminal. Here, the cash register or POS system and the payment terminal communicate with each other. The amount to be paid is automatically transferred from the cash register to the terminal.

    Cash register interfaces, or communication protocols, facilitate communication between cash register and payment terminal.

    Why is the cash register interface independent of terminal hardware?

    From the outside, you cannot see which cash register interface a POS terminal uses.Communication between the cash register and the terminal is never about the hardware of the terminal, but always about the communication protocol used.
    To enable communication between the payment terminal and the cash register, it is necessary to integrate the matching cash register interface respectively the correct communication protocol into the cash register software.

    The problem? Cash register software tends to support only a handful of communication protocols, which limits the connection of new POS terminals.

    Why are there so many different cash register interfaces?

    Initially, solutions for cashless payment processing at the POS developed independently in different countries, partly because the regulatory requirements for the payment process are different in each country. Even if the globalisation of the economy has progressed in many areas, the prevailing cash register interfaces throughout the world still differ today.

    Internationally different cash register interfaces

    In Europe alone, each country has its own prevailing cash register interfaces, not to mention a range of other communication protocols that are also used occasionally in the respective countries. Acquirers also develop their own cash register interfaces, some even new ones.

    Click here to find out more on the role of acquirers as market participants with regard to cashless payment.

    Depending on an acquirer’s market penetration, such in-house developed cash register interfaces can spread even across several countries.

    CountryWidely used cash register interfacesOccasionally used cash register interfaces
    GermanyZVT (in varying degrees)OPI, Nexo Retailer Protocol
    SwitzerlandWorldline TIMZVT, OPI, Nexo Retailer Protocol, own cash register interfaces by certain acquirers
    AustriaWorldline TIMZVT, OPI, Nexo Retailer Protocol, own cash register interfaces by certain acquirers
    FranceC3Own cash register interfaces by certain acquirers
    Benelux countriesOPI, VICOwn cash register interfaces by certain acquirers
    PolandOwn cash register interfaces by certain acquirers
    Czech RepublicOwn cash register interfaces by certain acquirers
    DenmarkOwn cash register interfaces by certain acquirers

    Nationally different cash register interfaces

    Internationally, the cash register interfaces that are primarily used differ considerably. But even within national borders there is hardly any standardisation worth mentioning.

    This is also partly in the interest of the acquirers who, by using a certain interface, make it more difficult for retailers to switch. If retailers want to use another payment terminal to process cashless payments, they have to integrate the right interface into their POS system first in order to be able to communicate with another terminal at all. The development effort resulting from it can be enormous. For users of POS-Terminals to gain more freedom and flexibility, there have been repeated attempts to standardise the cash register interface – nationally and internationally.

    Attempt to establish an international standard: the OPI interface

    Wouldn’t it be great to have one standard cash register interface throughout the world? There have been in fact several attempts to establish such a global standard – by international organisations such as ISOIECIFSF or IEEE, but also by large companies. New cash register interfaces should be flexible and state-of-the-art, yet only few have managed to establish in the market.

    One exception is the OPI interface of Wincor-Nixdorf, which has been used e.g. in the Benelux countries, Austria, and Switzerland.

    Attempt to establish an international standard: the ZVT interface in Germany

    Within Germany, the manufacturers of payment terminals have actually agreed on a common cash register interface standard: The ZVT protocol, or ZVT for short. By the way, ZVT is derived from the original name of the device: ZahlungsVerkehrsTerminal (German for Payment Transaction Terminal).

    As the resolution of the abbreviation ZVT suggests, this protocol has been in use for many years. Technologically, there are now much more advanced communication protocols than the ZVT interface. It doesn’t change the fact, however, that to a certain extent it has become a standard in Germany.

    The specifications of the ZVT cash register interface to download

    Would you like to know the exact specifications of the ZVT cash register interface? Not a problem! The Association of terminal manufacturers (Verband der Terminalhersteller) in Germany has provided a detailed document for download.

    To the download of the ZVT cash register interface

    ZVT interface leaves room for interpretation

    Now it’s fair to assume that the allegedly standardised ZVT interface makes it easier to switch to a new payment terminal within Germany and thus give retailers more flexibility.

    In practice, however, switching terminals is still difficult in most cases as the ZVT interface leaves plenty of room for interpretation. The protocol specification alone is about 200 A4 pages long. If this room for interpretation was to be used for the development of actual interface software, the results, in turn, would not be universally compatible.

    Especially if the retailer requires very specific features, there are sometimes also add-ons that exceed the standard defined in the protocol specification by far.

    So even if the basic specifications of the ZVT interfaces are similar, the room for interpretation means that switching to a new payment terminal can involve a great deal of development effort – unless you use a universal interface such as Pepper by treibauf, which makes it extremely easy to connect across all existing communication protocols.

    ZVT interface as byte-based protocol

    The ZVT interface is a classic byte-based communication protocol. In the early days of cash register interfaces, a list of fields was defined. Some must be transferred mandatorily with each call, while others can be transferred optionally.

    For each of these commands, the value range and the coding of the subsequent user data is fixed.

    The fixed definitions of value ranges and encodings have led to a limitation of the ZVT interface. For the communication protocol to meet newer requirements, it has been expanded by the ability to use TLV (Type Length Value Container) containers which are significantly more flexible with regard to the structure and content of the transmitted data.

    Click here to find out more about the use and function of TLV containers.

    Advantages of the ZVT interface

    • The ZVT interface is commonly used in Germany
    • Even beyond German borders various different European acquirers offer this type of cash register interface
    • The ZVT interface has many different functions, including:
      • All kinds of payment transactions
      • Cancellations
      • Reservations (Hotels)
      • Vouchers
      • Mobile prepaid recharge

    Disadvantages of the ZVT interface

    • There is great room for interpretation when implementing this communication protocol, which makes a universal connection difficult
    • if retailers require very specific features, there are also add-ons that exceed the standard far by
    • The interface is not enabled for cloud computing
    • The interface is not safe in terms of transmissions via the public internet

    Advantages of universal cash register interfaces

    So what are the alternatives, if even in the land of standardisations there is no real universal standard for cash register interfaces?

    The answer is a universal interface which not only “masters” more than 150 different communication protocols, but also all common interpretations and add-ons that exceed the standard of these communication protocols by far.

    This interface called Pepper makes it quick and easy to connect new terminal models (or cash register interfaces) at home and abroad. It also gives retailers more flexibility and independence when it comes to choosing the acquirer they want to work with.


    • Cash register systems and POS terminals communicate via a cash register interface
    • There are many different cash register interfaces at home and abroad
    • Thus, connecting new terminals to cash register system becomes more difficult
    • Within Germany, the ZVT interface is sort of considered standard (except for some niche protocols)
    • Different interpretations of the ZVT interface, however, often make the connection of a new payment terminal extremely difficult
    • Universal interfaces master all common communication protocols and therefore make it easier to connect new payment terminals
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