Determining the

Number of Readings

FETCh(ed)

The commands used to fetch (retrieve) readings from memory are:

FETCh[<chan >]?

If the <chan > parameter is ’1’ or is not specified, the readings (pre- and post-arm) from channel 1 and from the most recent INITiate - ARM - TRIGger sequence are retrieved. If the <chan > parameter is ’2’, the readings from channel 2 are retrieved.

FETCh[<chan >]:RECover?

This command is used to retrieve readings from non-volatile (battery-backed) memory following a power failure. The command is also used to retrieve readings after a digitizer configuration change or reset. Attempting to fetch (retrieve) readings using FETCh[<chan >]? following any of these conditions would cause error 230 "Data corrupt or stale" to occur.

If the <chan > parameter is ’1’ or is not specified, the readings from channel 1 are recovered. If the <chan > parameter is ’2’, the readings from channel 2 are recovered.

The number of readings that FETCh? retrieves can be determined two ways. The first way is with the command:

FETCh[<chan >]:COUNt?

Separating Pre- and Post-Arm Readings

This command returns the total number of readings (pre- and post-arm) that the FETCh? command will retrieve. Since both channels always take the same number of readings, either channel can be specified.

The second way to determine the number of readings is to multiply the arm count by the trigger count. These two counts can be obtained from the queries:

ARM:STARt:COUNt?

(arm count)

TRIGger:STARt:COUNt?

(trigger count)

The number of pre-arm readings and the number of post-arm readings are related to the total reading count as follows:

post-arm readings = total readings - pre-arm readings

The FETCh[< chan >]:COUNt? command and the ARM:STARt:COUNt? and TRIGger:STARt:COUNt? queries described previously return the total number of readings. The pre-arm count is determined by taking the absolute value of the query:

140 Understanding the HP E1429 Digitizer

Chapter 3

Page 140
Image 140
HP E1429A manual Determining Number of Readings FETChed, Separating Pre- and Post-Arm Readings