The information in this article applies to:
- Microsoft Visual FoxPro for Windows, versions 5.0, 5.0a
SYMPTOMS
When an instance of the Microsoft Communication Control (MSComm Control)
receives a CHR(0) it ignores that character and all characters that follow.
RESOLUTION
One of the following suggestions should resolve this problem:
- Set the InputLen property of the Microsoft Communication Control to 1
and read one character at a time.
- If possible, do not send CHR(0) or NULL to the Microsoft Communication
control.
STATUS
Microsoft is researching this problem and will post new information here in
the Microsoft Knowledge Base as it becomes available.
MORE INFORMATION
The Microsoft Communication Control truncates all characters following, and
including, a CHR(0) or NULL that is passed to its Input. This occurs when
the "NullDiscard" of the Microsoft Communication control set to ".F."
Steps to Reproduce Behavior
- Connect two computers via a NULL Modem cable. For example, COM1 port of
a computer (PC1) connected to the COM1 port of another computer (PC2)
via a Null Modem Cable.
- On PC1, place the following commands into a Visual FoxPro program and
then execute it, to create and run a form that sends serial output
using the MS Communication Control:
OUTFORM = CreateObject("comtst1")
OUTFORM.Show
READ EVENTS
DEFINE CLASS COMTST1 AS FORM
Top = 7
Left = 88
Height = 239
Width = 288
DOCREATE = .T.
Caption = "Form1"
Name = "Form1"
OUTVAL = .F.
ADD OBJECT TEXT1 AS TEXTBOX WITH ;
HEIGHT = 37, ;
LEFT = 29, ;
TOP = 84, ;
WIDTH = 229, ;
Name = "Text1"
ADD OBJECT Olecontrol1 AS Olecontrol WITH ;
OLECLASS="MSCOMMLib.MSComm.1",;
TOP = 12, ;
LEFT = 0, ;
HEIGHT = 100, ;
WIDTH = 100, ;
NULLDISCARD = .F., ;
Name = "Olecontrol1"
ADD OBJECT Command1 AS CommandBUTTON WITH ;
TOP = 37, ;
LEFT = 104, ;
HEIGHT = 27, ;
WIDTH = 84, ;
CAPTION = "Open Port", ;
TABINDEX = 2, ;
Name = "Command1"
ADD OBJECT Command2 AS CommandBUTTON WITH ;
TOP = 133, ;
LEFT = 104, ;
HEIGHT = 27, ;
WIDTH = 84, ;
CAPTION = "Send", ;
Name = "Command2"
ADD OBJECT Command3 AS CommandBUTTON WITH ;
TOP = 193, ;
LEFT = 104, ;
HEIGHT = 27, ;
WIDTH = 84, ;
CAPTION = "Exit", ;
Name = "Command3"
PROCEDURE Command1.Click
IF This.CAPTION="Open Port"
ThisForm.Olecontrol1.PORTOPEN=.T.
This.Caption = "Close Port"
Else
ThisForm.Olecontrol1.PORTOPEN=.F.
This.Caption = "Open Port"
EndIf
ENDPROC
PROCEDURE Command2.Click
*** Send CHR() representation of numbers entered ***
OVAL1 = ALLTRIM(ThisForm.TEXT1.Value)
OVAL2 = "chr(" + STRTRAN(OVAL1, " ", ")+chr(") + ")"
ThisForm.Olecontrol1.OUTPUT=&OVAL2
ENDPROC
PROCEDURE Command3.Click
ThisForm.Release
CLEAR EVENTS
ENDPROC
ENDDEFINE
- Switch to PC2 and place the following code into a Visual FoxPro program
and execute it to create and run a form that receives serial input using
the MS Communication Control:
INFORM = CREATEOBJECT("comtst2")
INFORM.SHOW
READ EVENTS
DEFINE CLASS comtst2 AS FORM
Top = 5
Left = 1
Height = 216
Width = 410
DoCreate = .T.
Caption = "Form1"
Name = "Form1"
inval1 = .F.
inval2 = .F.
ADD OBJECT Olecontrol1 AS OleCONTROL WITH ;
OleCLASS="MSCOMMLib.MSComm.1",;
TOP = 12, ;
LEFT = 12, ;
HEIGHT = 100, ;
WIDTH = 100, ;
NAME = "Olecontrol1", ;
NullDiscard = .F., ;
RThreshold = 10
ADD OBJECT Command1 AS CommandBUTTON WITH ;
TOP = 24, ;
LEFT = 150, ;
HEIGHT = 27, ;
WIDTH = 84, ;
CAPTION = "Open Port", ;
NAME = "Command1"
ADD OBJECT Edit1 AS EditBOX WITH ;
FONTNAME = "Arial", ;
HEIGHT = 64, ;
LEFT = 24, ;
TOP = 72, ;
WIDTH = 252, ;
NAME = "Edit1"
ADD OBJECT Command2 AS CommandBUTTON WITH ;
TOP = 108, ;
LEFT = 298, ;
HEIGHT = 27, ;
WIDTH = 84, ;
CAPTION = "Clear Text", ;
NAME = "Command2"
ADD OBJECT Command3 AS CommandBUTTON WITH ;
TOP = 72, ;
LEFT = 298, ;
HEIGHT = 27, ;
WIDTH = 84, ;
CAPTION = "View Input", ;
ENABLED = .F., ;
NAME = "Command3"
ADD OBJECT Command4 AS CommandBUTTON WITH ;
TOP = 178, ;
LEFT = 150, ;
HEIGHT = 27, ;
WIDTH = 84, ;
CAPTION = "Exit", ;
NAME = "Command4"
PROCEDURE Command1.CLICK
IF This.CAPTION="Open Port"
ThisForm.Olecontrol1.portopen=.T.
This.CAPTION = "Close Port"
ThisForm.Command3.ENABLED=.T.
ELSE
ThisForm.Olecontrol1.portopen=.F.
This.CAPTION = "Open Port"
ThisForm.Command3.ENABLED=.F.
ENDIF
ENDPROC
PROCEDURE Command2.CLICK
ThisForm.Edit1.VALUE = ""
ENDPROC
PROCEDURE Command3.CLICK
ThisForm.inval1 = ThisForm.Olecontrol1.INPUT
FOR i = 1 TO LEN(ThisForm.inval1)
ThisForm.inval2 = ASC(SUBSTR(ThisForm.inval1, i, 1))
ThisForm.Edit1.VALUE=ThisForm.Edit1.VALUE+;
" "+ALLTRIM(STR(ThisForm.inval2))+" "
ENDFOR
ENDPROC
PROCEDURE Command4.CLICK
ThisForm.RELEASE
CLEAR EVENTS
ENDPROC
ENDDEFINE
- Click Open Port on the InForm form on PC2 to open the communication port
on that computer.
- Switch to PC1 and click Open Port on the OutForm form on PC1 to open the
communication port on that computer.
- Select the edit box on OutForm and enter the following numbers into
the first line:
15 255 13 10 25
NOTE: Ensure that the numbers are entered with a space between them but
with no space before the first (15) and after the last number
(25).
- Click SEND on OutForm to send the numbers.
- Switch to PC2 and click View Input on InForm. Look at the contents of
the edit box.
NOTE: The characters sent by OutForm are displayed in the edit box of
InForm. So, the characters are being received and recognized by
MS Communication Control on the receiving end.
- Click Clear Text to clear the edit box.
- Go back to PC1 and insert a "0" between the second and third number
in the edit box of OutForm so that the entries look like the following:
15 255 0 13 10 25
- Click SEND on OutForm to send the numbers.
- Switch to PC1 and click View Input. Look at the contents of the edit
box.
NOTE: Only the first and the second numbers (15 255), sent by OutForm on
PC1, are displayed in the edit box of InForm. The "0" and the
numbers following it are not displayed. This illustrates that
after a receiving CHR(0) or NULL that the MS Communication Control
ignores that particular character and all characters following it.
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