The PC2USD™

PC2USD is a hardware interface with software and source code that allows a programmer to control the spirals on a series of vending machines. Dispenses products based on PC serial port commands. By using the Universal Satellite Device feature of the MDB protocol, the PC can now dispense by row and column in any USD MDB equipped vending machine

Example for a Universal Satellite Device

PC2USD Screen Shot
Software and source code (VB 6.0) are included with the PC2MDB

Power requirements
24 to 35 Vdc
90 ma Typical
300 ma Maximum
Environmental
Operating Temp 32°F to 158°F
0°C to 70°C
Storage Temp -22°F to 165°F
-30°C to 74°C
Relative Humidity 5% to 95% Non-condensing
Physical Weight
< 1 lb
Physical Dimensions
Length 4.0 inches Width 3.0 inches Height 1.1 inches
Connector Info
PWR 24-35V Pin 2 +24Vdc Nominal
Pin 4 Ground
MDB Pin 1 +24Vdc Nominal
Pin 2 Ground
Pin 3 N/C
Pin 4 MDB Receive Data
Pin 5 MDB Transmit Data
Pin 6 Common

RS-232 Pin 1 N/C
Pin 2 PC Transmit Data
Pin 3 PC Receive Data
Pin 4 DTR
Pin 5 Ground
Pin 6 N/C
Pin 7 N/C

Pin 8 CTS
Pin 9 N/C
LED/Jumper Designations
D2 +5Vdc
D3 MDB Activity
D4 PC Activity
D6 Pulse Output Activity
Switch 1: Mode Select 1
Switch 2: Mode Select 2

Figure-2 Connector Pin Outs

Install the PC2USD™

It is time to install the PC2USD™ itself and move on to the testing phase. Installation is relatively simple; there are only three connections that must be made for full functioning of the device. There are connectors on the edge of the board. One cable plugs into a 24VDC power supply. The 6-pin Molex connects to the VMC. The final connector is a DB-9 and connects into the back of the computer. There should be an open port on the back of the computer labeled “SERIAL2” or “COM2.”

Software

Overview

When the master/VMC has data to send we check the mode bit to differentiate between ADDRESS bytes and DATA bytes. The upper five bits (MSB) of the Address Byte are used for addressing. The lower three bits of the Address Byte contain peripheral specific commands. This will allow up to eight instructions to be embedded in the first byte of block.

The PC2USD sends information generated by the VMC device directly to the PC via RS-232 serial communication. The PC receives Data from the PC2MDB in ASCII and transmits in Binary. It responds to polls issued by the VMC. PC2USD will ACK only the polls, and commands issued to correct addresses. The PC2USD then forwards the commands to the PC. Once the data has been processed, the PC sends back another set of instructions to the PC2USD, which forwards these instructions to the VMC only when desired poll/polls have been received. The information sent to the PC is send as bytes in hexadecimal. The first byte sent is the device ID. For example 30 XX means that a bill validator has sent information. Whereas 08 XX means that a coin mechanism has sent data. Consult your manual for commands specific to your MDB device. We have included command sets for various MDB devices in this document. Please note that all examples of source code are written in MS Visual Basic 6.0

PC2USD Software Communication

Receive

Use an interrupt driven comm event on the appropriate port. Settings are 9600-8-1-None. Set the receive threshold to 1. Empty the contents of the receive buffer as soon as there is at least one character ready. See the sample source code provided on CD-ROM for an example.

******************************************************************
'Receive
******************************************************************

Case comEvReceive 'Received RThreshold # of Chars

Do While MSComm1.InBufferCount > 0

For ii = 1 To 500000 'Added this delay to allow the input buffer to read
Next ii 'entire contents. Approx 50mSec delay

MDB_Input$ = MSComm1.Input

MDBData.AddItem "USD: " & MDB_Input$

    smdb10$ = Mid$(MDB_Input$, 1, 14)                '#10 copies the input string keeping the original.
    smdb11$ = Mid$(smdb10$, 1, 2)                    '#11 determines what the response from USD, based on NAMA MDB chapter 9
    smdb12$ = Mid$(smdb10$, 4, 5)                    '#12 is the row and column
    smdb14$ = Mid$(smdb10$, 13, 2)                   '#14 is the USD resoponse code.

Select Case smdb11$

Case ("08")

'response after a status request, NAMA MDB chapter 9.8

Select Case smdb12$

Case ("01 00") 'row and column

Select Case smdb14$

                    'following strings- error codes
                    '00 = coil is working and no errors
                    '01 = coil selection sold out
                    '02 = motor is jammed
                    '04 = motor not detected
                    '05 = invalid

Case ("00")
Command15.BackColor = QBColor(10) 'green- OK

Case ("01")
Command15.BackColor =QBColor(14) 'yellow- error

Case ("02")
Command15.BackColor = QBColor(14)

Case ("04")
Command15.BackColor =QBColor(12) 'red- don't use

Case ("05")
Command15.BackColor = QBColor(12)

End Select

Transmit

Use an interrupt driven comm event on the appropriate port. Settings are 9600-8-1-None. Set the transmit threshold to 1. Send the address of the device followed by the command parameters.

********************************************************************
'TRANSMIT
********************************************************************

Private Sub Command16_Click()

'Here is an example of a typical command concatenated using the '&'
'In this case it is the command to spin coil row 2, column 0

MDB_output_string = Chr$(&H43) & Chr$(2) & Chr$(2) & Chr$(&H0)

'Set DTR high telling the PC2MDB that we wish to transmit

MSComm1.DTREnable = True 'start handshaking

'Send detail to the list box so the user sees something

lstActionLog.AddItem "Spin Coil (2,0)"

lstActionLog.ListIndex = lstActionLog.ListCount - 1

Exit Sub

End Sub

Select Case MSComm1.CommEvent

Case comEvCTS 'Change in the CTS line

'this is the output routine for transmitting outbuffersize set to 34 bytes

MSComm1.Output = MDB_output_string

For ii = 1 To 500000 'Added this delay to allow the output buffer to clear Next ii 'Transmit entire contents. 50mSec delay

MSComm1.DTREnable = False

Handshaking XE "Handshaking"

When the PC has data to send to a slave device the following is required for sending this data:

Send DTR high (DTR.Enabled=TRUE)
On Change in CTS line (generated by the VMC) set output buffer=string to be transmitted
Place contents of string in output buffer and transmit
Set DTR low after transmitting entire string

Notes: Place the string to be transmitted in a temporary variable and then place the temporary variable in the output buffer.
**********************************************************************
'HANDSHAKING
**********************************************************************

Since we have the contents to be transmitted in a temporary string (MDB_output_string) and we ‘have set DTR high (comInterface.DTREnable = True) we now wait for a comm. Event to be generated ‘namely a change in the CTS line :

   Case comEvCTS      'Change in the CTS line
                      'this is the output routine for transmitting
                      'outbuffersize set to 32 bytes
   comInterface.Output = MDB_output_string
'END transmit one character on change of CTS line

‘At this point the data has been sent to the output buffer of the serial port UART. By setting ‘the Send Threshold to 1 we fire a comm. Send event when the entire contents of the output buffer ‘have been sent and set DTR low to indicate that we have completed transmission. For example(4)

Case comEvSend 'There are SThreshold number of characters in thetransmit buffer
comInterface.DTREnable = True