MDB Communication Protocal
Introduction
This doc defines a serial communication protocol between the application running on Q3v and MDB Vending machine. Overall,the q3v low level hardware will forwarding the mdb request from the vendg machine,and forward to the Android application as serial data, When the app tackle all the request serial data, the q3v pos could be regarded as a MDB cashless slave device. And also,the application could request some config command, e.g. "get firmware version",Therefore the protocol is 2-way-direction, and there is a mode byte indicates the direction.
Serial Protocol Packet Definition
Serial Port parameters
- Baud rate 115200
- 8bit, 1 stop bit, and no parity
Packet format
| Start code | Length | mode | Data | Checksum | End code |
- Start code size 1 byte, always be 0x09
- Length size: 1byte, the number bytes of mode, data, and checksum.
- Mode size: 1, 0x00 means a master request packet, 0x01 means a slave response packet, other value is prohibited.
- Data size: n bytes. The data could be raw MDB commands, such as SETUP, VEND(please refer the <Multi-Drop Bus Protocol V4.3>for detials).
Or the MIB control commands, such as GET VERSION, SET PARAMETER.
- Checksum size: 1byte, using LRC algorithm, input data were "mode, data"
MDB Forwarding mechanism
The q3v will forward all the MDB cashless device commands,except the the POLL command,the request and response procedure can be described in following steps:
- VMC Send MDB request to q3v
- q3v receive the step 1 data,get rid the 9th mdb mode bit,fill into serial packet data part,sending the serial packet to application.
- The application will listen to to the serial port all the time,after receiving step 2 serial data,unwrap it to mdb request data,handle it, and wrap its mdb response into serial packet, sending to q3v
- q3v get the step 3 data, unwrap to mdb response data, add mdb mode bit,forwarding to mdb master.
- mdb master handle the mdb slave response
Taking the RESET for example
- VMC -> q3v: 0x110 0x10
- q3v -> app: 0x09 0x04 0x00 0x10 0x10 0xE0 0x0D
- app -> q3v: 0x09 0x04 0x01 0x00 0x00 0xFF 0x0D
- VMC -> MIB: 0x00 0x100
- VMC -> MIB: 0x00
A typical MDB transacrion flow
