Time Interval and Frequency Counter

30 Programming Commandssynchronization to be achieved using thesynchronization commands.There is no need to wait between commands. TheSR620 has a 256 character input buffer andprocesses commands in the order received. If thebuffer fills up the SR620 will hold off handshakingon the GPIB and attempt to hold off handshakingon RS232. If the buffer overflows the buffer will becleared and an error reported. Similarly, theSR620 has a 256 character output buffer to storeoutput until the host computer is ready to receiveit. If the output buffer fills up it is cleared and anerror reported. The GPIB output buffer may becleared by using the Device Clear universalcommand.The present value of a particular parameter maybe determined by querying the SR620 for itsvalue. A query is formed by appending a questionmark "?" to the command mnemonic and omittingthe desired parameter from the command. Ifmultiple queries are sent on one command line(separated by semicolons, of course) the answerswill be returned in a single response line with theindividual responses separated by semicolons.The default response terminator that the SR620sends with any answer to a query is carriagereturn-linefeed on RS232 and linefeedplus EOI on GPIB. The RS232 terminator may bechanged using the ENDT command, while theGPIB terminator is fixed. All commands returninteger results except as noted in individualcommand descriptions.Examples of Command FormatsTERM 1, 1 Sets the A channel inputimpedence to 1 Mohm (2parameters).TERM? 1 Queries the A inputtermination (query of 2parameter command)..*IDN? Queries the deviceidentification (query, noparameters).STRT Starts a measurement noparameters).MODE 1 ; MODE? Sets mode to width (1) thenqueries the mode.Detailed Command Listsequence consists of parameters. Multipleparameters are separated by commas.Parameters shown in {} are optional or may bequeried while those not in {} are required.Commands that may be queried have a questionmark? in parentheses (?) after the mnemonic.Commands that may ONLY be queried have a ?after the mnemonic. Commands that MAY NOTbe queried have no?. Do not send ( ) or { } as partof the command.Variable i is an integer that selects an inputchannel for the command:i Channel0 External input1 A input2 B inputThe variables j,k,l,m, and n are also integers. Thevariable x is a real number.All variables may be expressed in integer, floatingpoint or exponential formats ( ie., the number fivecan be either 5, 5.0, or .5E1).IMPORTANT NOTE: ALL of the front panelsettings to the left of the "CONFIG" button, and theJITTER type (Allan variance or standard deviation)are properties of the present operating mode andare saved when the mode is changed. Thus, if themode is changed the previous settings of theseparameters in the new mode will automatically beset. The programmer MUST be careful to set allrelevant parameters each time the mode ischanged to prevent conflicts between thepresumed and actual states of the instrument.Trigger Control CommandsLEVL(?)i {,x}The LEVL command sets, or reads, the triggerthreshold for channel i. If the SR620 is in theautolevel mode, this command will turn off theautolevel mode and set the desired threshold.The trigger level set by the LEVL command willremain in effect until the front panel knob isrotated. In remote mode the front panel knob isignored. If the trigger level is queried (LEVL? i )the answer returned is a floating point number with2 digits to the right of the decimal point, forexample, -1.07.The four letter mnemonic in each commandsequence specifies the command. The rest of theSR620 Universal Time Interval Counter