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Communicating with Anritsu's IEEE-488.2 Non-Compliant Instruments Application Note IEEE - 488.2 Non-Compliance Introduction The purpose of this application note is to recognize the difficulties associated with remotely controlling some of Anritsu's instruments via the GPIB bus. This note will define the exact cause of the difficulties and then describe a way to reliably communicate with these troublesome models. Problem Statement GPIB Bus Command Termination Most Anritsu instruments can be remotely One method of signaling the end of a controlled by a computer using the GPIB bus. command is to add one additional special The GPIB bus has been a mainstay in the Test character, known as the EOS (End of & Measurement world since 1965 and was Statement) character. The most common EOS standardized by publication of the IEEE-488 is "new line", otherwise known as "line feed" specification in 1975. There have been two or ASCII 0x0A. The receiving instrument can major enhancements to this standard, with the simply continue to accept bytes until it receives latest being IEEE-488.2 in 1987. the designated EOS character, and then act on all of the preceding bytes. The EOS technique The GPIB bus is used to send a series of is the easiest to implement by both the 8-bit bytes between instruments or between transmitting and receiving devices, but it is a computer and an instrument. Most often the slightly inefficient because an extra character bytes transmitted are standard ASCII letters must be transmitted with each command. The and numbers. For example, if a computer wants EOS technique can also become a problem if to set the frequency in a signal generator to the data to be passed over the GPIB bus 12345 Hz, the computer might send the includes the EOS byte. For example, reading a command "FREQ 12345". Upon receipt of this long series of binary bytes from an A-to-D command, the signal generator will immediately converter may eventually hit upon all possible switch to the new 12345 frequency. That binary values, including the special EOS value. sounds simple enough, but how did the This would cause the transmission to be instrument know when it had received the prematurely terminated. entire command? Why didn't it switch to a new frequency of 123 after receiving the characters The alternative to using a special termination "FREQ 123"? How did it know to wait until the character is to use a termination signal outside "5" was received? This raises the whole issue the normal path of the data bytes. The GPIB of command termination on the GPIB bus. bus is defined as 24 parallel lines, of which 8