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The HP 70843A Network performance analyzer, is capable of generating PRBS, zero substitution, variable mark density, as well as user-programmable test patterns. In zero substitution test patterns, zeros can be substituted for data to extend the longest run of zeros in patterns. The longest run can be extended to the pattern length -1. The bit following the substituted zeros is set to 1. In variable mark density, the ratio of 1s to total bits in patterns can be set to 1/8, 1/4, 1/2, 3/4, or 7/8. User-programmable patterns can range in length from 1 bit to 8M bits. The 70843A also allows for alternate test pattern function, in which the user can switch between two equal length patterns, each up to 4,194,304 bits, under the control of a front panel key, GPIB, or the auxiliary input port; changeover is synchronous with the end of a word. Two methods of controlling pattern changeover are available, one shot and alternate. A clock input at the pattern generator provides multiple features such as setting frequency, setting frequency step, measuring frequency, and setting the output level of the clock source. The clock input is capable of handling frequencies from 100 MHz to 12.5 GHz with amplitudes from 450 to 900 mV pp. The Agilent 70943A provides both normal and parallel data output. Other data output capabilities include data high level adjustment, and data amplitude adjustment. Delay v clock adjustment and vertical data-eye cross-over adjustment are also available. The outputs can have an external termination voltage of 0/-2V or can be AC coupled. An external attenuator can be set from 0 to 40 dB for a 0V termination. For normal and parallel data, independant control is available for high level, amplitude, and On/Off functions. Errors can be added to data with three modes of operation: single, which introduces single errors on demand; fixed, which introduces fixed ratios of errors in 10^n bits, where n = 3, 4, 5, 6, 7, 8, and 9; in external error operation, a single error is injected in the transmitted test pattern on each rising edge at the external inject input port. In addition to data and inverted data outputs, the 70843A provides clock and parallel clock outputs. The user can adjust the clock high level, the clock amplitude, whether the output external termination is 0/-2V or AC coupled. An external attenuator can be set from 0 to 40 dB at 0V termination voltages. Independent control of high level and amplitude is available for clock and parallel clock outputs. Four subrate parallel data outputs and one subrate clock output are available. Subrate data and clock are at 1/4 the main data and clock rate, and subrate data is inverted relative to the main data output. The user can adjust high-level and amplitude for both clock and data signals. Clock and data signals can be set to ECL, and the external termination voltage on these outputs can be 0/-2V or the outputs can be AC coupled. The Agilent 70843A provides an electrical trigger synchronous with the pattern. IT can be configured as a pattern or clock trigger, where the pattern trigger position can be set. In divide clock mode, the trigger is a square wave at the clock rate divided by 32 or 8. The auxiliary input port allows for the control of user-programmable alternate test patterns or to force the data to a fixed low level. The instrument will output one of two patterns at the end of their pattern. The auxiliary input controls which pattern is output in one of two modes. In oneshot mode, a rising edge on the auxiliary input inserts a single version of B pattern into repetitions of pattern A. In alternate mode, the logic state of the signal at the auxiliary input determines the output pattern, depending on whether the signal is a logic 0 or 1. If an alternate pattern is not selected, an active (TTL low) signal at the auxiliary input gates the data to a logic 0 at the next 32 bit boundary. The 70843A provides clock and data error detection. At the clock input error detector, the termination can be either 0 or -2V, and the input frequency can be measured.
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