Top Ten SCPI Programming Tips for Signal Generators - Rohde ...

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Command Synchronization Timeout A timeout denotes the time period the controller waits for a response from the instrument. If the specified period has elapsed, the communication is aborted with a (timeout) error. 4.2.2 Query OPC Status in the Event Status Register If you activate a time-consuming operation and wait for completion with *OPC, a timeout could occur before the operation is finished and you do not receive the returned “1”. In addition, the test program is blocked while waiting with *OPC. It is not possible to process other (not interdependent) commands in the meantime or to communicate with other instruments. Thus, for time-consuming operations, you can avoid blocking the communication by sending the operation complete command *OPC: SCPI sequence: *CLS *OPC and afterwards polling the operation complete status in the event status register with the following command: SCPI query: *ESR This query returns the content of the event status register and afterwards clears the content. The event status register comprises eight bits. We are interested in bit 0 – the operation complete bit. If an *OPC command is sent and if all commands sent before *OPC have been executed, then this bit is set to 1. In contrast to the *OPC query, the *OPC command does not block command processing. Event status register Bit number Meaning 0 (LSB) Operation complete 1 Not used 2 Query error 3 Device-dependent error 4 Execution error 5 Command error 6 User request 7 (MSB) Power on 1GP79_1E Rohde & Schwarz Top Ten SCPI Programming Tips for Signal Generators 10
Command Synchronization The *ESR command returns an eight-bit value and afterwards clears all bits. For example, let us assume the response is 32. The eight-bit binary representation of 32 is 00100000. The most significant bit (MSB) of the event status register is bit number 7. Thus, bit number 5 is 1, all other bits are 0. In this example, a command error has occurred. After readout, bit number 5 is set to 0. We are now interested in bit number 0 of the event status register. To “extract” the OPC bit from the received eight bits apply a bitwise “AND” operation with the decimal number 1 (eight-bit binary representation is 00000001). Bit number 0 (LSB) 1 2 3 4 5 6 7 (MSB) OPC x x x x x x x 1 0 0 0 0 0 0 0 bitwise AND OPC 0 0 0 0 0 0 0 ESR 1 Bitwise AND A logical AND operation is performed on each pair of corresponding bits. In each pair, the result is 1, if the first bit is 1 and the second bit is 1. Otherwise, the result is 0. Effectively, the bitwise AND operation with the decimal 1 sets all bits to 0 except the OPC bit. The result is either 00000001 in case the OPC bit is 1, or 00000000 in case the OPC bit is 0. In decimal representation, the result is either 1 (meaning the operation is complete) or 0 (meaning the operation is not yet complete). Poll the event status register periodically until the returned OPC bit is 1. 4.2.2.1 Polling the ESR Using a Loop The easiest way to poll the event status register is to use a loop with a delay function (such as the sleep() function in C). It is important to use a non-busy-wait delay function in order not to block the test program, or more precisely the currently active thread. Busy-waiting Busy waits waste CPU resources that could be used to execute different tasks instead. Generally, busy waits should be avoided. Delays should be implemented using nonbusy waits that take up only little CPU time, as they spend most of their time “asleep”. Non-busy waits cause the active thread to be suspended from execution and pass the CPU resources on to other threads. 1GP79_1E Rohde & Schwarz Top Ten SCPI Programming Tips for Signal Generators 11
Page 1 and 2: Application Note C. Tröster 04.201
Page 3 and 4: Error! No text of specified style i
Page 5 and 6: Top Ten Tips 2 Top Ten Tips Automat
Page 7 and 8: Program Start At program start, we
Page 9: Command Synchronization Sometimes
Page 13 and 14: Command Synchronization 4.2.2.2 Pol
Page 15 and 16: Command Synchronization 4.2.4.2 Pol
Page 17 and 18: Error Queries 5 Error Queries Query
Page 19 and 20: Speed Optimization 6 Speed Optimiza
Page 21 and 22: Speed Optimization The same method
Page 23 and 24: Waveform Transfer & Loading 7 Wavef
Page 25 and 26: Example Script 8 Example Script In
Page 27 and 28: Example Script status = rs_send_com
Page 29 and 30: Programming Lists and Sweeps 9 Prog
Page 31 and 32: Miscellaneous Tips 10 Miscellaneous
Page 33 and 34: Miscellaneous Tips 10.2 Instrument
Page 35 and 36: Miscellaneous Tips 10.4 Code Debugg
Page 37: About Rohde & Schwarz Rohde & Schwa

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