Serial Port -
MDB Vendor Protocol: WK-MDB Module
(multi-drop bus) serial port protocol evolved to become the standard
protocol between the control components in vending machines in the
mid 1990's. The protocol specifies how the vending machine
controller talks to the coin changer, the bill validator, the display, and
installed card readers.
The WK-MDB Module is designed to provide the electrical and protocol
interface between a vending machine controller (VMC) and a WR88
Its three diagnostic LED indicators provide visual operational
information that may be helpful during installation and for
troubleshooting problems. The enclosure dimensions are 3.0" L x 2.5" W x 1.0" H (76mm x 63mm x
25mm) and has integral mounting ears.
There is an
RJ-11 telephone style connector on the right side of the enclosure to plug in the
WR88 Wicket Reader. There is an attached 16" cable assembly on the left hand side of the enclosure
with two connectors: one to connect to the vending machine
controller, and the other which is just a daisy-chain pass-through
connector for connecting other devices to the multi-drop bus.
MDB Spec V3.0
supports two cashless devices. The address select switch
located on the left side of the enclosure
configures the WK-MDB Module as one device or the other. The
valid cashless addresses are 0x10 (address 1) and 0x60 (address 2).
This provides a means for compatibility in a system already having a
credit card device installed. Any change made to the address select
switch will not take effect until the next
module reset through a power cycle or if the vending machine
controller commands a bus reset.
Note: The Wickets Administrator
software utility must be used
to configure the WR88 Wicket Reader to enable the MDB Vendor
Protocol to properly communicate with the WK-MDB-Module.
Programming for for information about setting
the configuration parameters for the WR88.
A typical vending
transaction for a customer would proceed something like this:
1.) A customer
walks up to the vending machine to buy something using his Wicket.
2.) As in other
transactions where money is first deposited, the Wicket is first
read to start the sequence.
3.) The machine
controller determines if the customer has enough to buy the lowest
customer is prompted to make an item selection for vending.
customer is prompted to read his Wicket again to debit it and
complete the transaction.
6.) The machine
controller tells the Wicket Reader how much to debit the next
7.) The Wicket
Reader blinks white to indicate a Wicket debit transaction is
pending for the amount.
customer reads his Wicket again, the amount is debited and the
reader blinks green.
completed debit transaction is communicated back to the vending
vending machine controller vends the item to the customer.
11.) If the
item fails to vend, the vending machine controller sends a refund to
the Wicket Reader.
12.) The Wicket
Reader blinks white to indicate a pending refund transaction for the
customer reads his Wicket again, the amount is refunded, and the
Wicket Reader blinks green.
14.) If the
same Wicket is not presented to take the refund within 30 seconds,
the Wicket Reader goes back to the idle blue color and saves the
refund information for some future time when the Wicket is again
presented and completes the transaction then.
The MDB Specification does not guarantee that you can just plug the
WK-MDB Module and a WR88 Wicket Reader into just any vending machine
and expect it to work. The vending machine controller may not be
capable of communicating with a second cashless payment device, or
it may have an incompatible implementation of the communication
sequence details. Please contact IDX sales for compatibility