Sniffing 9-bit Multi Drop Bus commands on PIC24
By Beep Technologies Pte Ltd
MDB (Multi Drop Bus) Protocol is a popular protocol for American & European vending machines to communicate with their peripherals (e.g: Coin, Bill and Card devices)
- https://www.ccv.eu/wp-content/uploads/2018/05/mdb_interface_specification.pdf
- This code enables one to analyze the incoming data from the 9 bit serial channel for debugging purposes
As the MDB Protocol regretfully lacks a reliable SOH/ETX method, most implementations work by performing a checksum on the incoming bytes to differenciate incoming payloads. There might be scenarios where the checksum is equal to an incoming byte, leading to truncation of data.
We use a time-based logic which measures the inter-byte interval to reliably differenciate commands. In fact we use a more advanced version of this code in our commercial MDB/VCCS+JVMA (yes, the pesky Japanese protocol) solutions for implementing the 10H and 60H cashless device.
The MDB Sniffer approach is also useful in obtaining data from the coin/cash peripherals by implementing the CASH SALE protocol.
- It is a good learning experience (especially for students who previously only dealt with Arduino)
- It has a pretty good IDE
- The Japanese use it in their vending machine equipment
- It cannot be easily reverse engineered (Search 抄板解密打样 “Copy board, rip firmware & make a prototype” on Taobao)
Reverse engineering is an epic (and costly) journey to the center of one’s soul.
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This is released under the Mozilla Public License 2.0