View Full Version : MDB (Multi-Drop Bus) & Stamp

10-31-2009, 01:47 AM
I am using a BS2px to control a host of vending machine type coin dispensers. Has anyone worked with MDB or ccTalk on the stamp? I am stumped on circuit connection and communication with the devices within Pbasic.

Here is a link for MDB protocol

Here is the link for ccTalk

I have followed the directions in part 3 of cctalk to build a serial interface. I connected it into my board but when I get to use header 167 to dispense I have no idea what security algorithm they are talking about. If ccTalk is too complicated, I will go with MDB, but I havent seen how to connect it with the stamp and what baud rate combo to use because it has an extra mode bit.


Don M
11-02-2009, 09:01 PM
I have not done anything in regards to having a stamp control any coin mechs or validators via MDB but I somewhat understand the MDB protocol. If you are looking to control these devices you will want to stick with MDB as it is the protocol of choice for the last 10 years in vending. MDB4 was just released this year as an ungrade to accomodate the newer validators that pay back notes rather than change (they call them bill recyclers).

What makes MDB hard to implement is that it uses a 9600 baud 9 bit data stream. The timing is rather critical.

I use one of the devices attached below to communicate via a pc serial port to MDB devices and this could easily be done with the basic stamp as well. You just need to send a simple command via SEROUT and receive in via SERIN.

11-03-2009, 01:13 AM
Thanks very much for the reply.
I would like to avoid purchasing another component for this project. Do you know how I might interface with the MDB directly and how (if possible) I would format my serout & serin for 9 bit?


Don M
11-03-2009, 01:39 AM
Doc- No I don't. Sorry. Maybe some others here may be able to help.

11-05-2009, 02:51 AM
anyone else have any experience using MDB?

05-11-2010, 08:01 PM
Hi docwisdom! (http://forums.parallax.com/member.php?u=57630)

Me too I'm interrested in·vending m. control and MDB. Have you done any progresses meanwhile?

03-20-2013, 03:36 PM
MDB can be interfaced directly to a UART, or bit banged with GPIO.
The rx line needs a small pullup resistor and the tx line will need an amplifier to supply the minimum source current of 100mA @ 4v.

Our company also offers a product called the MDBPro

It handles the complexity of the MDB protocol and passes simple ASCII or modbus signals over serial line.
The MDB layer is completely masked from the host device.

03-20-2013, 03:54 PM
...please be aware that this thread is nearly 3 years old.