How connect PC Embedded to MDB (Vending Machine)

Yup, totally. Interesting thread ;-)

I wouldn't do this as a byte-wise buffer device, but rather as a higher level gateway. Implement the MDB state machine in the microprocessor to behave as the communications gateway, peripheral, or bus master as required/desired. The side facing the PC could run at a higher baud (or even over a different medium) and would not necessarily use the MDB message structure.

Personally, on the side facing the PC I'd try very hard to push everything into a plain-text format. Easy to monitor and log, simple to debug, and it can be digested by lots of analysis tools without a separate binary -> ASCII translator pass.

I don't think one should try to do the parity trick with a virtual serial port.

However, some of the USB serial chips may be flexible enough to implement a 9-bit mode without resorting the parity trick.

Alternatively, some of the USB-capable microcontrollers certainly are.

And then there's the possibility of a parallel interface chip, and a small CPLD.

None of these would be presented to the host PC as a serial port, but instead as a custom interface.

:

Yes, I want that my pc embedded will be a Slave.

I want that my pc embedded will be as a Communications Gateway (Section 8) for to receive all the information from the VMC. It is possible?

regards. Juan.

Hi Juan,

Yes it is possible, but everything I mentioned previously remains the same.

To be honest we have not looked at Section 8, we are mainly involved in coin/note validation. However, nothing else changes. The device you want to build is still just a device that must meet the standard MDB interface specification.

Connection to the MDB bus for you as a device is much simpler than that of a host. You can get away with a couple of opto couplers, just like in the sample schematic in that section 4. You would be for eg slave 1.

PhilW

Yes I agree with you that would be the better way to go. However, it is stepping away from the MDB protocol concept. It also adds a lot of work and maintainance.

PhilW

Hi,

I'm not aware of any USB chips that support full 9 bit mode. Probably for a couple of reasons (off the top of my head). They are designed emulate a PC serial port, the CDC spec does not really support it. The CDC spec is rather broad in its possible applications, but the section that is utilised for virtual serial ports is based on the modem type interface. As far as I'm aware modems don't use 9bit.

Even though some USB-capable chips are able to support 9bit serial, supporting it through the USB is another question.

PhilW

PhilW, Have you anyone schematic to make a adapter MDB to RS232 or any pc port (usb, rj45, etc...)??

Thanks you!

Juan.

Anybody Can answer me?

But.. have you considered using the Executive Protocol ? Of course, it depends on the function you have to implement, anyway it is less difficult, even if it isn't possible to connect directly the PC seria port with the vending machine.

Talking about mdb I've found only the PC2MDB product, but I haven't used it. Let us know if you try it..

I'm unsure if there are affordable off-the-shelf USB to 9 bit adapters (Black Box probably has an adapter for $$$).

Atmel AVR and Microchip PIC chips (such as the PIC18F14K50, PIC18F66J50 as featured in the October 2008 Circuit Cellar magazine) have 9 bit UARTS and USB 2.0 on chip, but require your own programming. Manufacturer's Application Notes and user support might give you all the building blocks, perhaps entire programs to handle the problem.