Physical and Environmental
Diagrams and pin-outs
LED's and Jumpers
Indicators and jumper settings
Compatible devices
List of vending devices verified
User's Guide
On-line version of the User's Guide including MDBLAB™
Sample Source Code
Complete interface spec for the programmer
Download Source Code
Free software development kit
Download Executable
Complete MDBLAB executable/installable

The MDB2PC™  

Computer Peripheral for interfacing MDB protocol devices with a personal computer


The MDB2PC™ is a Computer Peripheral for interfacing vending machine protocol used by various devices including: Dollar Bill Validators, Coin Acceptors, Coin Dispensers, Smart Cards, Foreign Currency etc.This describes the Interface Protocol for the MDB2PC™ Hardware circuit. The MDB2PC is a microprocessor controlled hardware interface with embedded firmware that converts the MDB protocol to an RS232 protocol.

What is MDB and why do I need the MDB2PC™?

MDB stands for "Multi-Drop Bus" and is a protocol developed by vending machine industry. The "Multi-drop Bus" (MDB) protocol is not compatible with the standard RS-232 PC protocol and therefore a hardware and software interface is necessary. The MDB2PCis a microprocessor controlled hardware interface with embedded firmware that converts the MDB protocol to an RS232 protocol and also performs the necessary voltage conversion. The MDB2PC also relieves the Polling requirements thereby allowing the same PC to perform other tasks.

The MDB2PC is necessary to interface the industry standard MDB Vending machine protocol to a standard PC because:

  • The MDB uses 11 Bits and a nine (9) bit byte.
  • The polling requirements for the various MDB devices are excessive (20-200 ms).
  • A non-dedicated PC can not meet the polling requirements.
  • The MDB2PC™ takes care of the polling requirements and generates an interrupt on the serial port of the PC.
  • This methods allows the PC to perform normal operations and respond to interrupt driven comm events in the UART buffer.
  • All data from an MDB device is available to the PC.
  • Additionally, all commands can be sent to the MDB device from the PC (ie. dispense, write to smart card etc...)

The MDB2PC™ interfaces any MDB vending device (6-pin molex/5pin MTA) to the PC via the serial port (DB-9).The MDB2PC™ protocol is compatible with standard RS-232 Protocol.

Benefits and Features

Up to eight (8) MDB compliant devices may be attached to a single MDB2PC™. The programming interface is user-friendly and may be downloaded for free. Sample source code is available and may be freely distributed. We also offer a Software Developer's Kit

Coin Acceptors/Dispensers and Foreign Currency

Any MDB compliant device may be interfaced to a PC. This now makes it possible to accept and dispense any coin types including foreign currency and Euro Dollar (when available)

Smart Card Reader

MDB compliant smart card readers can now be accessed.


Power requirements
24 to 35 Vdc
90 ma Typical
300 ma Maximum
Operating Temp 32F to 158F
0C to 70C
Storage Temp -22F to 165F
-30C to 74C
Relative Humidity 5% to 95% Non-condensing
Physical Weight
< 1 lb
Physical Dimensions
Length 4.0 inches Width 3.0 inches Height 1.1 inches
Connector Info
PWR 24-35V Pin 2 +24Vdc Nominal
Pin 4 Ground
MDB Pin 1 +24Vdc Nominal
Pin 2 Ground
Pin 3 N/C
Pin 4 MDB Receive Data
Pin 5 MDB Transmit Data
Pin 6 Common

RS-232 Pin 1 N/C
Pin 2 PC Transmit Data
Pin 3 PC Receive Data
Pin 4 DTR
Pin 5 Ground
Pin 6 N/C
Pin 7 N/C
Pin 8 CTS
Pin 9 N/C
LED/Jumper Designations
D2 +5Vdc
D3 MDB Activity
D4 PC Activity
D5 Status 1
D6 Status 2
Jmp1 Mode Select 1
Jmp2 Mode Select 2
Estimated 250,000 Hrs.