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MDB payment systems normally are set up to operate in one of two modes: authorization first/idle mode or selection first/always idle mode. Each mode has a number of states which indicate the progress of the vending cycle:
Authorization first/idle mode states:
OFF - MDB-USB Interface is not connected to a payment system
INIT - reader is disabled and showing the "cash only" screen
IDLE - reader displays cashless animation waiting for user to present their card
CREDIT - card has been scanned, reader shows the "select a product" screen and waits for the VMC to request the amount to charge the card
VEND - reader is waiting for payment authorization
RESULT - payment is accepted
Selection first/always idle mode states:
OFF - MDB-USB Interface is not connected to a payment system
INIT - reader is disabled and showing the "cash only" screen
IDLE - reader displays the product selection screen and waits for VMC to request money
VEND - reader is waiting for user to pay
RESULT - payment is accepted
Example of a simple vending cycle in authorization first/idle mode
State
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Description
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IDLE
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The reader is enabled and is displaying the authorization screen with an animation inviting the user to scan their credit card. When the user scans their card the state changes to CREDIT
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CREDIT
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The reader displays the "select a product" screen and waits for the user to select a product. When a product is selected the state changes to VEND. If a timeout occurs before the user selects a product the transaction is cancelled and the state returns to IDLE
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VEND
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The reader is obtaining authorization for the requested payment. If the payment is authorized the state changes to RESULT. If it fails the transaction is cancelled and the state returns to IDLE
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RESULT
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The payment has been authorized and the reader is waiting for the vending machine to dispense the product. When the product has been dispensed the vending machine sends and END command and the state changes to IDLE. If the vending machine is unable to dispense the product it can send a failure message to cancel the transaction
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Example of a simple vending cycle in selection first/always idle mode
State
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Description
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IDLE
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The reader is enabled and is displaying the "select a product" screen. When the user selects a product the vending machine requests payment from reader and the state changes to VEND
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VEND
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The reader displays the "authorization" screen and waits for the user to present their card. If the user presents their card and the payment is authorized the state changes to RESULT. If a timeout occurs before the user presents the card or the payment is not authorized or the vending machine cancels the selection the transaction is cancelled and the state returns to IDLE
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RESULT
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The payment has been authorized and the reader is waiting for the vending machine to dispense the product. When the product has been dispensed the vending machine sends and END command and the state changes to IDLE. If the vending machine is unable to dispense the product it can send a failure message to cancel the transaction
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