READ?
READ?
Syntax
34970A Syntax: READ?
34972A Syntax: READ? [(@<scan_list>)]
Description
This command changes the instrument's triggering system from the "idle" state to the "wait-for-trigger" state. Scanning will begin when the specified trigger conditions are satisfied following the receipt of the READ? command. Readings are then sent immediately to reading memory and the instrument's output buffer. On the 34970A, you must then receive the readings into your computer or the instrument will stop scanning when the output buffer becomes full. Readings are not stored in the instrument’s internal memory when using READ?. On the 34972A, the readings are always sent to memory and they will still be available after READ? finishes.
Used With:
- 34901A 20 Channel Multiplexer (2/4-wire) Module
- 34902A 16 Channel Multiplexer (2/4-wire) Module
- 34907A Multifunction Module (digital input and totalizer)
- 34908A 40 Channel Single-Ended Multiplexer Module
Parameters
Name Type Range of Values Default Value <scan_list> Scan List One or more channels, as shown:
(@310) - channel 10 on the module in slot 300.
(@305:310) - channels 05 through 10 on the module in slot 300.
(@202:207,209,302:308) - channels 02 through 07 and 09 on the module in slot 200 and channels 02 through 08 on the module in slot 300.
This is a required parameter.
Remarks
- Sending the READ? command is similar to sending the INITiate command followed immediately by the FETCh? command.
- You can store up to 50,000 readings in memory and all readings are automatically time stamped. If memory overflows, the new readings will overwrite the first (oldest) readings stored; the most recent readings are always preserved. In addition, bit 9 is set in the Questionable Data Register's condition register (see Status System Introduction).
- For scanning measurements using the multiplexer modules, an error is generated if the internal DMM is disabled (see INSTrument:DMM command) or not installed in the mainframe. The internal DMM is not required for operations on the digital modules.
- The instrument scans the list of channels in ascending order from slot 100 through slot 300 (channels are re-ordered as needed).When you specify a range of channels in the <scan_list>, the channels are always sorted in ascending order. Therefore, (@109:101) will always be interpreted as 101, 102, 103, etc.
- Once you initiate a scan, an error will be generated if you attempt to change any measurement parameters (CONFigure and SENSe commands) or the triggering configuration (TRIGger commands). To abort a scan in progress, send the ABORt command.
- Each reading is returned with some combination of measurement units, time stamp, channel number, and alarm status information, depending on the settings set by the FORMat:READing commands. The time stamp is either in relative format (time in seconds since the beginning of the scan) or absolute format (time of day with date, based on the instrument's clock as set by the SYSTem:DATE and SYSTem:TIME commands). The choice of absolute and relative time is determined by the FORMat:READing:TIME:TYPE command.
- The READ? query is not valid with the *TRG command (used with TRIGger:SOURce BUS command for software triggering).
- The instrument clears all readings from memory after a Factory Reset (*RST command) or after an Instrument Preset (SYSTem:PRESet command).
- If you specify a <scan_list> with this query (34972A only), it will overwrite the current scan list.
Return Format
The command sends readings directly to reading memory and the instrument's output buffer (with formatting as set by the FORMat:READing commands). Multiple responses are separated by commas.
Examples
The following program segment shows how to use the READ? command with the CONFigure command. The ROUTe:SCAN command puts the two channels into the scan list (and redefines the scan list). The READ? command places the instrument in the "wait-for-trigger" state, scans the specified channels when the rear-panel Ext Trig Input line is pulsed low, sends the readings to reading memory and the instrument's output buffer.
CONF:VOLT:DC 10,0.003,(@103,108) !Configure channels
ROUT:SCAN (@103,108) !Define the scan list
TRIG:SOUR EXT
READ? !Applies to the present scan list
Typical Response: +4.27150000E-03,+1.32130000E-03
See Also