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== Bugs in Vending Machines ==
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TCN vending machines and other white labelled machines charge $655.35 for every product

tcn

Problem

A TCN vending machine charges customer $655.35 on credit card, but cash payment is ok.

Story

Some (or all of them?) TCN vending machines charge customer $655.35 on credit card, but cash payment is ok. This is because TCN vending machine initialised all cashless price to 0xFFFF after reset, and this causes the cashless pricing to $655.35, or 65.535 if your currency is 3-decimal.

Solution

  1. Credit card reader should immediately abort these abnormal cashless transactions.
  2. TCN’s firmware developers should study MDB protocol better.
  3. Change your credit card reader to walk around this bug.