MDB Communication Protocal
Introduction
This manual describes the serial communication protocol between Q3 Pos and MDB Interface Board, which will be short as “MIB” in follow content.
The basic baud rate of serial port is set as 115200
As the Q3 POS could be receive command from MIB as a slave, and also could send command to MIB as a master (e.g., send “begin session” command to inform the MDB VMC it’s ready for pay), a mode byte was added in serial frame to show if a command is slave response or a master request.
The request command always anticipates a response command except the checksum is wrong, or the incorrect serial format, in another word, the slave will use silence as a NAK. Please refer to the documentation for specific commands and details.
Serial Protocol Packet Definition
Serial Port Parameters
Baud rate: 115200
Data format: 8 bits, 1 stop bit, no parity
Packet Format
Start code: size 1 byte, always be 0x09
Length: size 1 byte, the number bytes of mode, data, and checksum.
Mode: size 1 byte, 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. Or the MIB control commands, such as GET VERSION, SET PARAMETER.
Checksum: size 1 byte, using LRC algorithm, input data were "mode, data"
End code: size 1 byte, always be 0x0D.
Specifics
MDB Forwarding Mechanism
When the MIB receive the VMC request, it removes the MDB mode bit, fill into serial packet data area, and transmit to serial port. In the opposite direction, the MIB receive the response, it unwraps the packet, and adding mode bit to the tail bytes, sending to the VMC, wait for the acknowledge.MIB will forward all the MDB cashless device commands (MDB spec section 7), except VMC request Poll.
Example: RESET
VMC -> MIB: 0x110 0x10
MIB -> Q3V: 0x09 0x04 0x00 0x10 0x10 0xE0 0x0D
Q3V -> MIB: 0x09 0x04 0x01 0x00 0x00 0xFF 0x0D
MIB -> VMC: 0x00 0x100
VMC -> MIB : 0x00
Application Notes
Focus on steps 2 and 3 in the MDB Forwarding Mechanism.
The application handles all cashless commands except POLL.
The cashless reader initiates a begin session command to notify the VMC when ready for a transaction.
MDB raw data includes its checksum byte, distinct from the serial frame checksum.
A Typical MDB Transaction Flow
Protocol Command Definition
Please refer to the documentation for specific commands and details.
Common MDB Forwarding Command
This command forwards raw MDB commands (including MDB CHK), with the MDB mode bit removed.
Request Packet:
| Mode | Data |
|---|---|
Request 00H | VMC Request Command (Reset,Setup,Reader,Expansion,Vend) |
Response Packet:
| Mode | Data |
|---|---|
Response 01H | Peripheral Response |
Example: MIB -> Q3V 09 04 00 10 10 E0 0D
Q3V -> MIB 09 04 01 00 00 FF 0D.
Begin Session Command
When the application is ready for a transaction, it issues a begin session command to inform the VMC master. This marks the beginning of a transaction. Balance amount is 2 bytes; if balance does not exist, fill with 0xFF. This command follows MDB spec definition but is initiated by the app.
Request Packet:
| Mode | Data |
|---|---|
Request 00H | Begin Session (03H) + Funds Available + MDB Checksum |
Response Packet:
| Mode | Data |
|---|---|
Response 01H | ACK 00H |
Example: Q3V -> MIB 09 06 00 03 00 64 67 32 0d
MIB -> Q3V 09 03 01 00 ff 0d
Session Cancel Request(0x04)
The application can end a payment session by issuing a session cancel request command. The POS acts as the master during this command.
Request Packet:
| Mode | Data |
|---|---|
Request 00H | Cancel Session Req(04H) + Funds Available + Checksum |
Response Packet:
| Mode | Data |
|---|---|
Response 01H | ACK 00H |
Demo
PC Simulation Testing Guide
There're two types of MDB RS232 box, please confirm which one are you testing:
Testing Guide for blue MDB232 box
Testing Guide for black MDB-RS232 box
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