Agilent Technologies L4400 Podręcznik Użytkownika Pobierz pdf (Strona 230)

218 L4400 User’s Guide

8 L4450A 64-Bit Digital I/O with Memory and Counter

Initiated Measurement Mode

Measurements such as frequency, period, duty cycle, and pulse width

require an initiate command and a gate. The

SENSe:COUNter:INITiate

command is used to initiate (arm) the measurement. The measurement is

gated by either an internal (default) or external gate source. For

measurements the external gate acts like an external trigger which triggers

the internal gate timer.

The gate source is set using the SENSe:COUNter:SOURce command. 

The default gate source is INTernal. The gate is the aperture over which

the signal data is gathered. When the gate is internal, the measurement

begins as soon as the

INITiate command is received.

Since the measurements are all derived from the same basic measurement,

you can retrieve the measured frequency, period, duty- cycle, and pulse

width from the same initiated and gated measurement. For example, the

following commands set the counter to measure the input signal for 1 ms

using the internal gate. The frequency, period, duty cycle, and pulse width

are returned as floating point numbers.

CONF:COUN:FREQ 1e-3, (@1301)

SENS:COUN:INIT (@1301)

SENS:COUN:FREQ? (@1301)

SENS:COUN:PER? (@1301)

SENS:COUN:PWID? (@1301)

SENS:COUN:DCYC? (@1301)

The CONFigure:COUNter:FREQuency command parameter sets the internal

gate time (to 1e- 3 or 1 ms in the above example). You can also set the

gate time using the

SENSe:COUNter:GATE:TIME command.

Clock

The general- purpose clock output is derived from the internal time base.

The output clock is divided down from the time base clock such that:

Clock Output (Hz) = (time base frequency)/(divisor)

The time base frequency is 40 MHz. The divisor can be an integer from 

2 to 4

providing a range of 20 MHz to 10 Hz for the clock output. 

The valid values for the clock output rate are: 20 MHz, 13.33 MHz, 

10 MHz, 8 MHz, 6.667 MHz, ... 10Hz. The clock output frequency will round

to the nearest achievable frequency.

The commands used to control the clock output are:

SOUR:MOD:CLOC:FREQ {<freq>|MIN|MAX|DEF},<slot>

SOUR:MOD:CLOC {OFF|ON|0|1},<slot>

You can obtain the rounded value of the currently set clock frequency

using the following query.

1 2 ... 225 226 227 228 229 230 231 232 233 234 235 ... 280 281

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