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ESR

121User Manual 1175.7068.02 ─ 12

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Creating a response buffer

Since the DLL returns zero-terminated strings in responses, a string of sufficient

length must be created before the functions InstrRead() and ilrd() are called,

because Visual Basic inserts a length specification in front of the strings and this

specification is not updated by the DLL. The following two means of creating the

length specification for a string are provided:

Dim Rd as String * 100

Dim Rd as String

Rd = Space$(100)

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Creating Wrapper Procedures for Writing and Reading

Since the "VISA" functions require command and response strings and their corre-

sponding length in two separate parameters, the main program code is easier to

read and maintain if the read and write functions are encapsulated. Here, the pro-

cedure InstrWrite() encapsulates the function viWrite() and InstrRead()

encapsulates viRead(). In addition, these wrappers include status checking:

Public Sub InstrWrite(ByVal vi As Long, ByVal Cmd As String)

Dim status As Long

Dim retCount As Long

'Send command to instrument and check for status

status = viWrite(vi, Cmd, Len(Cmd), retCount)

'Check for errors - this will raise an error if status is not VI_SUCCESS

CALL CheckError(vi, status)

End Sub

Public Sub InstrRead(ByVal vi As Long, Response As String, _

ByVal count As Long, retCount As Long)

Dim status As Long

'Initialize response string

Response = Space(count)

'...and read

status = viRead(vi, Response, count, retCount)

'Check for errors - this will raise an error if status is not VI_SUCCESS

CALL CheckError(vi, status)

Brief Introduction to Remote Control

R&S ESR Series User Manual

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