Retrieving

Readings Using

READ?

Retrieving

Readings Using

FETCh?

The most common method of retrieving readings from the digitizer is using the READ? subsystem which consists of the command:

READ[<chan >]?

The <chan > parameters are:

1 - returns readings from channel 1 (default channel)

2 - returns readings from channel 2

READ? is equivalent to executing the following sequence of commands:

ABORt - aborts the readings after the arm count and trigger count is reached.

INITiate - places the digitizer in wait-for-arm state.

FETCh[<chan >]? - retrieves the readings from memory and places them on the VME (VXI data transfer) bus.

As a result, READ? is used for applications that require readings to be immediately available to a computer, rather than remaining in digitizer memory.

Because each READ? initiates the digitizer, executing READ1? followed by READ2? causes the digitizer to take two sets of measurements. If it is necessary to obtain readings from both channels during the same period, use INIT and FETCh? which are described in the next section.

One method of retrieving readings from memory involves the digitizer’s FETCh? command shown below. FETChing readings from memory places them on the VME (VXI data transfer) bus

(Figure 3-11).

FETCh[<chan >]? :COUNt? :RECover?

FETChing Readings from Memory

Recall that the HP E1429 digitizer samples both channels simultaneously and stores the readings as a single 24-bit number (Figure 3-8). Using the FETCh? command, each channel’s readings can be retrieved from memory individually.

Chapter 3

Understanding the HP E1429 Digitizer 139

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HP E1429A manual Read?, Retrieving Readings Using FETCh?, FETChing Readings from Memory