Agilent Technologies 16760A Burst, Has adjustable sampling positions on each input channel, 124

Chapter 4: Using the Logic Analyzer in Eye Scan Mode

Setting Up and Running Eye Scan Measurements

	A suitable qualification signal is rarely available. Instead, an extra
	circuit (added to the SUT, in a probe adapter, or other convenient
	location) is usually required to decode read/write commands and
	generate the qualifier. The analyzer samples the qualification signal at
	the beginning of each clock cycle (i.e. at the first of each pair of data
	transfers). The analyzer can be configured to treat either the rising
	edge or the falling edge of the clock as the first edge of each clock
	cycle. The qualifier should remain stable for the entire duration of each
	burst.
	Also, the qualifier must be pipelined (delayed) by one clock cycle
	before transmittal to the analyzer. The qualifier may be driven after the
	clock edge (i.e. you may use the output of a flip flop) since the analyzer
	has adjustable sampling positions on each input channel.
NOTE:	The time range available for eye scan when the qualifier is in use depends on
	the sampling position of the qualifier input in the analyzer. The range is
	increased as the position is made later (as the sample position moves from
	before the clock edge to after it).
	The available eye scan range in 800 Mbs eye scan mode always begins at -4 ns
	and goes through +8 ns + tQualSample, where tQualSample is the qualifier's
	sample position as shown in the eye finder display (see Analyzer Setup,
	below). The adjustment range for tQualSample is from -2.5ns through +2.5 ns.
	Putting it all together, the figure below shows the qualifier timing for a
	pair of eight-transfer data bursts, the first of which is to be qualified for
	eye scan and the second of which is to be ignored. The example shows
	a system with a clock cycle beginning with a rising edge and a high-true
	qualifier level. The qualifier signal to the analyzer is assumed to be the
	output of a pipeline register and is therefore sampled by the analyzer
	after the rising edge of the clock.

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