Multi-Drop Bus / Internal Communication Protocol

Last updated

Multi-Drop Bus / Internal Communication Protocol (MDB/ICP) is the latest, US-European iteration of a multidrop bus computer networking protocol used within the vending machine industry, currently published by the American National Automatic Merchandising Association and supported by the European Vending Association and the European Vending Machine Manufacturers Association. It is based on earlier protocols (also known as MDB in the US) dating back to at least the early 1990s. [1] [2]

Contents

Mechanism

The multidrop bus used by vending machine controllers to communicate with the vending machine's components, such as a currency detector, is also called MDB (for Multi-Drop Bus). In use since the 1980s, it is now an open standard of the National Automatic Merchandising Association, or NAMA. The devices communicate in a single-master, multiple-slave configuration using the MDB protocol, which is based on a Motorola [ specify ] 9-bit UART implemented as an 8-bit data value with an additional mode bit. The mode bit differentiates between ADDRESS and DATA bytes. The master sends messages containing one address byte and a variable number of data bytes. The bus "slave devices" listen for an address, and if it matches their address that slave device will process the message and respond to the master. [3] Though 9-bit compliant UARTs are not popular in PCs, they can be found in many microcontrollers.

The physical connection is realized as a serial bus with a fixed data rate of 9600 baud . There are just 2 communications signals plus the essential common-ground reference signal. The TX signal goes from the MASTER to every SLAVE device. The RX signal goes from every SLAVE device to the MASTER device. Both signals have pull-ups. The bus is driven at every transmitter by an open collector transistor driver, and isolated at each receiver with an opto-isolator - though cable harnesses carrying the communication signals may also carry 24-volt power and ground signals to devices, meaning the devices may not be isolated from each other as they share the same power bus. Some devices, however, may have alternate power supplies, especially devices with motors and high current needs such as vintage bill acceptors or currency detector devices.

History

MDB originated as a proprietary bus used by CoinCo for their coin-acceptors in the late 1980s and was deployed in high volume in vending machines for Coca-Cola. Coke forced CoinCo to open-source it in 1992 to increase competition, and NAMA released the first version of the standard in 1995, allowing other vendors to compete for the coin-acceptor portion of the vending machines (CoinCo and Mars were the 2 major suppliers in North America at the time) and also enabled alternative payment schemes (e.g. Smartcard based) to be connected to existing vending machines.

Bus addressing is based on the device type only, which allows for a very simple protocol stack, as no initial enumeration needs to be performed.

Timeline

See also

Related Research Articles

Bus (computing) System that transfers data between components within a computer

In computer architecture, a bus is a communication system that transfers data between components inside a computer, or between computers. This expression covers all related hardware components and software, including communication protocols.

Universal asynchronous receiver-transmitter Computer hardware device

A universal asynchronous receiver-transmitter is a computer hardware device for asynchronous serial communication in which the data format and transmission speeds are configurable. It sends data bits one by one, from the least significant to the most significant, framed by start and stop bits so that precise timing is handled by the communication channel. The electric signaling levels are handled by a driver circuit external to the UART. Two common signal levels are RS-232, a 12-volt system, and RS-485, a 5-volt system. Early teletypewriters used current loops.

I²C Serial communication bus

I2C (Inter-Integrated Circuit, eye-squared-C), alternatively known as I2C or IIC, is a synchronous, multi-controller/multi-target (controller/target), packet switched, single-ended, serial communication bus invented in 1982 by Philips Semiconductors. It is widely used for attaching lower-speed peripheral ICs to processors and microcontrollers in short-distance, intra-board communication.

Serial communication Type of data transfer

In telecommunication and data transmission, serial communication is the process of sending data one bit at a time, sequentially, over a communication channel or computer bus. This is in contrast to parallel communication, where several bits are sent as a whole, on a link with several parallel channels.

The Serial Peripheral Interface (SPI) is a synchronous serial communication interface specification used for short-distance communication, primarily in embedded systems. The interface was developed by Motorola in the mid-1980s and has become a de facto standard. Typical applications include Secure Digital cards and liquid crystal displays.

Profibus Communications protocol

Profibus is a standard for fieldbus communication in automation technology and was first promoted in 1989 by BMBF and then used by Siemens. It should not be confused with the Profinet standard for Industrial Ethernet. Profibus is openly published as part of IEC 61158.

The System Management Bus is a single-ended simple two-wire bus for the purpose of lightweight communication. Most commonly it is found in computer motherboards for communication with the power source for ON/OFF instructions.

1-Wire Device communications bus system

1-Wire is a device communications bus system designed by Dallas Semiconductor Corp. that provides low-speed data, signaling, and power over a single conductor.

LIN is a serial network protocol used for communication between components in vehicles. It is a single wire, serial network protocol that supports communications up to 19.2 Kbit/s at a bus length of 40 meters. The need for a cheap serial network arose as the technologies and the facilities implemented in the car grew, while the CAN bus was too expensive to implement for every component in the car. European car manufacturers started using different serial communication technologies, which led to compatibility problems.

The Q-bus, also known as the LSI-11 Bus, is one of several bus technologies used with PDP and MicroVAX computer systems previously manufactured by the Digital Equipment Corporation of Maynard, Massachusetts.

The HART Communication Protocol is a hybrid analog+digital industrial automation open protocol. Its most notable advantage is that it can communicate over legacy 4–20 mA analog instrumentation current loops, sharing the pair of wires used by the analog-only host systems. HART is widely used in process and instrumentation systems ranging from small automation applications up to highly sophisticated industrial applications.

A multidrop bus (MDB) is a computer bus in which all components are connected to the electrical circuit. A process of arbitration determines which device sends information at any point. The other devices listen for the data they are intended to receive.

CANopen is a communication protocol and device profile specification for embedded systems used in automation. In terms of the OSI model, CANopen implements the layers above and including the network layer. The CANopen standard consists of an addressing scheme, several small communication protocols and an application layer defined by a device profile. The communication protocols have support for network management, device monitoring and communication between nodes, including a simple transport layer for message segmentation/desegmentation. The lower level protocol implementing the data link and physical layers is usually Controller Area Network (CAN), although devices using some other means of communication can also implement the CANopen device profile.

Polling, or polled operation, in computer science, refers to actively sampling the status of an external device by a client program as a synchronous activity. Polling is most often used in terms of input/output, and is also referred to as polled I/O or software-driven I/O. A good example of hardware implentation is a watchdog timer.

Digital Addressable Lighting Interface (DALI) is a trademark for network-based products that control lighting. The underlying technology was established by a consortium of lighting equipment manufacturers as a successor for 1-10 V/0–10 V lighting control systems, and as an open standard alternative to several proprietary protocols. The DALI, DALI-2 and D4i trademarks are owned by the lighting industry alliance, DiiA.

ccTalk is a serial protocol in widespread use throughout the money transaction and point-of-sale industry. Peripherals such as the currency detectors for coins and banknotes found in a diverse range of automatic payment equipment such as transportation, ticketing, payphones, amusement machines, and retail cash management use ccTalk to talk to the host controller.

UNI/O

The UNI/O bus is an asynchronous serial bus created by Microchip Technology for low speed communication in embedded systems. The bus uses a master/slave configuration, requiring one signal to pass data between devices. The first devices supporting the UNI/O bus were released in May 2008.

In building automation, eBUS is a 2-wire digital serial data-bus communication interface used in heating and solar energy appliances, by mainly German manufacturers. It was originally proposed by the Karl Dungs company, and has since been adopted by several other manufacturers. The eBUS interface has also been used by home-automation enthusiasts to connect their domestic solar or heating system to a networked PC for monitoring or remote control.

I3C (bus)

MIPI I3C is a specification to enable communication between computer chips by defining the electrical connection between the chips and signaling patterns to be used. The standard defines the electrical connection between the chips to be a two wire, shared (multidrop), serial data bus, one wire (SCL) being used as a clock to define the sampling times, the other wire (SDA) being used as a data line whose voltage can be sampled. The standard defines a signalling protocol in which multiple chips can control communication and thereby act as the bus controller.

XID or Transducer ID™ is a device communications bus system designed by Airmar Technology Corp., US to enable an echosounder to identify the type of ultrasonic transducer being connected. This allows the echosounder to adjust for the specific properties of the transducer such as frequency, power rating, beam pattern.

References

  1. 1 2 "Multi-Drop Bus / Internal Communication Protocol - MDB / ICP - Version 4.2" (PDF).
  2. "Overview of Vending Machine Interfaces" (PDF). European Vending Association. 2012.
  3. "MDB Specification Version 4.2" (PDF). NAMA. Archived from the original (PDF) on 2015-06-27. Retrieved 2018-10-11.
  4. "MDB v4.3" (PDF).
  5. "Multi-Drop Bus / Internal Communication Protocol - MDB / ICP - Version 3.0" (PDF). Archived from the original (PDF) on 2018-05-17.