I did something very similar using DDE and EXCEL and had the same problems. Maybe I can tell you my example and give you some direction since I have never used DDE and ACCESS before.
Basically I set up a HOT TOPIC DDE link from Excel to a BIT in the PLC. Since I wanted the PLC to trigger a "log this information bit" in my Excel Sheet. So when the HOT DDE LINK changed, I used a VB Script or Excel command called .OnData. When the PLC changed the bit from 0 to 1, EXCEL seen this change on the worksheet called "INDATA', then ran my macro called "START".
Warning! Make sure that NO OTHER information is on the worksheet called INDATA. Because you want to make sure that it is dedicated to the PLC's bit changes and nothing else.
Sub Auto()
Worksheets("INDATA").OnData = "Start"
' A bit change from the PLC Hot Linked on INDATA
' will automaticly Run Macro (start).
End Sub
Once my macro "start" was running, a bunch of COLD DDE links were opened up and I starting reading information from registers in the PLC
and wrote them in the Excel Sheet.
More Comments after code below.............
Sub Start()
Dim lngRow As Long
Dim varCycle As Variant
Dim varLogging As Variant
Dim varResults As Variant
On Error GoTo Error
'opens a COLD DDE link
RSIchan = DDEInitiate("RSLinx", "M1138")
'assign PLC bit values to VB variant varibles
varLogging = DDERequest(RSIchan, "B3/163")
varCycle = DDERequest(RSIchan, "B3/161")
'close COLD DDE link
DDETerminate (RSIchan)
'check to see if the Cycle bit went to "1" if it did, excute read data
If varCycle(1) = "1" And varLogging(1) = "1" Then
'starts at row 3 of sheet
lngRow = 3
If Range("INDATA!A3").Value > 3 Then
'look up last cell and change position
lngRow = Range("INDATA!A3").Value
End If
'check until end of sheet
For lngRow = lngRow To 65500
'look for next empty cell
If Cells(lngRow, 1) = "" Then Exit For
'write current cell location to sheet INDATA
'rather than writing a loop to search on
'every cycle, by the time the log is at row 21,500
'it could take a long time to search the rows...
Range("INDATA!A3").Value = lngRow + 1
'add 1 to row "x" to check next row
Next
'opens a COLD DDE link
RSIchan = DDEInitiate("RSLinx", "M1138")
'there might be a better way to do this like
'using this somehow ???????? but I don't know how
'data = DDERequest(RSIchan, "f11:0,L7,C7")
'Range("[M1138.xls]LOG!R[x]C1:R[x]C7").Value = data
'read word F8:10 and load into a VB variant variable
f810data = DDERequest(RSIchan, "F8:10")
'read word F8:11 and load into a VB variant variable
f811data = DDERequest(RSIchan, "F8:11")
'read word F8:12 and load into a VB variant variable
f812data = DDERequest(RSIchan, "F8:12")
'read word F8:16 and load into a VB variant variable
f816data = DDERequest(RSIchan, "F8:16")
'read word F8:18 and load into a VB variant variable
f818data = DDERequest(RSIchan, "F8:18")
'read word F8:17 and load into a VB variant variable
f817data = DDERequest(RSIchan, "F8:17")
'read word F8:20 force check #1 and load into a VB variant variable
f820data = DDERequest(RSIchan, "F8:20")
'read word F8:21 force check #2 and load into a VB variant variable
f821data = DDERequest(RSIchan, "F8:21")
'read word F8:22 force check #3 and load into a VB variant variable
f822data = DDERequest(RSIchan, "F8:22")
'read word F8:23 force check #4 and load into a VB variant variable
f823data = DDERequest(RSIchan, "F8:23")
'read word F8:25, get PASS or FAIL status from PLC and load into a VB variant variable
varResults = DDERequest(RSIchan, "F8:25")
'close COLD DDE link
DDETerminate (RSIchan)
'write all values to cells
Cells(lngRow, 1).Value = f810data
Cells(lngRow, 2).Value = f811data
Cells(lngRow, 3).Value = f812data
Cells(lngRow, 4).Value = f816data
Cells(lngRow, 5).Value = f818data
Cells(lngRow, 6).Value = f817data
Cells(lngRow, 7).Value = f820data
Cells(lngRow, 8).Value = f821data
Cells(lngRow, 9).Value = f822data
Cells(lngRow, 10).Value = f823data
Range("INDATA!A4").Value = varResults
If Range("INDATA!A4").Value = 1 Then
Cells(lngRow, 11).Value = "PASS"
'copies the conditioinal format to the next cell
Range("K" & lngRow + 1).Select
Selection.Copy
Range("K" & lngRow + 2).Select
ActiveSheet.Paste
Application.CutCopyMode = False
End If
If Range("INDATA!A4").Value = 2 Then
Cells(lngRow, 11).Value = "FAIL"
'copies the conditional format to the next cell
Range("K" & lngRow + 1).Select
Selection.Copy
Range("K" & lngRow + 2).Select
ActiveSheet.Paste
Application.CutCopyMode = False
End If
If Range("INDATA!A4").Value = 0 Then
Cells(lngRow, 11).Value = "NO DATA"
End If
If Range("INDATA!A4").Value > 2 Then
Cells(lngRow, 11).Value = "ERR"
End If
'capture time and date stamp into column 8
Cells(lngRow, 12).Value = Now()
'scrolls the screen down automatically
'Range("A" & lngRow + 1).Select
End If
GoTo Done:
Error:
frmError.Hide
frmError.Show
'trying a timed form box, so disabled the old MESSAGE BOX here for now
'MsgBox ("Communications to PLC have been lost! Or Log Sheet is FULL! Can not log data anymore. Check PLC connection and wiring.")
Application.Run Macro:="ChkTime"
Done:
'check for date change, if so then save as new sheet
Application.Run Macro:="ChkTime"
End Sub
So maybe hopeful you might be able to use the same concept to trigger your access sheet.
If you want to download the whole EXCEL SHEET CODE, you can get that file at:
http://www.mrplc.com/cgi-bin/code/filedisplay.cgi?category=excel
Scroll down until you see:
Allen Bradley SLC500 DDE Link to Excel Logger 1.0
Ofcourse look at the Macro VB Scripts to see the code used in Module1.
Ignore all the PDF macros.
Good Luck,...