Agilent Technologies 8935 Series Manual do Utilizador descarregar pdf (Página 52)

52 Chapter 2

O:\Manuals\E6380A_Progguid\Book\Measrslt.fm

Methods For Reading Measurement Results

Background

One of the most common remote user interface operations performed on

an Test Set is to query and read a measurement result. Generally, this

operation is accomplished by sending the query command to the Test

Set, followed immediately by a request to read the requested

measurement result. Using the Agilent Technologies Rocky Mountain

BASIC (RMB) language, this operation would be written using the

OUTPUT and ENTER command as follows:

Example 2-1 Query Example

OUTPUT 714;"MEAS:RFR:POW?"

ENTER 714;Power

Using this programming structure, the control program will stay on the

ENTER statement until it is satisfied - that is - until the Test Set has

returned the requested measurement result. This structure works

correctly as long as the Test Set returns a valid measurement result. If,

for some reason, the Test Set does not return a measurement result, the

control program becomes “hung” on the ENTER statement and program

execution effectively stops.

In order to prevent the control program from becoming “hung”

programmers usually enclose the operation with some form of time-out

function. The form of the time-out will of course depend upon the

programming language being used. The purpose of the time-out is to

specify a fixed amount of time that the control program will wait for the

Test Set to return the requested result. After this time has expired the

control program will abandon the ENTER statement and try to take

some corrective action to regain control of the Test Set.

If the control program does not send the proper commands in the proper

sequence when trying to regain control of the Test Set, unexpected

operation will result. When this condition is encountered, power must

be cycled on the Test Set to regain control.

This situation can be avoided entirely by:

1. sending a Selected Device Clear (SDC) interface message to put the

Test Set’s HP-IB subsystem into a known state.

2. sending a command to terminate the requested measurement cycle.

These commands issued in this order will allow the control program to

regain control of the Test Set. Any other sequence of commands will

result in unexpected operation.

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Agilent Technologies 8935 Series Manual do Utilizador Página 52