HP E1429A manual Locating Segmented Readings, ARMSTARtCOUNt, Maximum Readings

Locating Segmented Readings

For segmented readings (SENSe:SWEep:OFFSet:POINts ≤ -3), the algorithm for locating the readings is similar to that for unsegmented readings, but is slightly more complicated. The number of memory segments is determined by the specified arm count (ARM:STARt:COUNt) as shown in Table 3-5.

Table 3-5. Arm Count Vs. Memory Segments

ARM:STARt:COUNt		Number of	Maximum Readings
		Memory	(TRIGger:STARt:COUNt)
		Segments
	1	1	524,288
	2	2	262,144
3	- 4	4	131,072
5	- 8	8	65,536
9 - 16		16	32,768
17	- 32	32	16,384
33	- 64	64	8,192
65 - 128		128	4096

NOTE: If the non-volatile mode of memory is enabled (MEMory:BATTery:STATe ON), then all of the maximum reading counts shown above decrease by four. These four memory locations in each segment hold the data necessary to recover all readings after a power failure.

The algorithm for determining where the first reading of each segment begins is:

first reading in segment = ending segment address - (num_readings - 1)

where num_readings = TRIG:COUN + pad, and pad are extra counts to make the total reading count divisible by 4. The memory partition composed of num_readings is circular, and if large amounts of pre-arm data (readings) are taken, the data keeps overwriting itself until the arm is received and the post-arm count finishes. NOTE that the actual desired starting point for retrieving data will be:

last_data_point_address - (TRIG_COUN - 1)

which in most cases will not be the starting address if the segment has wrapped around at least once with pre-arm data. The digitizer firmware keeps track of the last address used in each segment and automatically reads the data in the proper order when a FETCh?, VME bus transfer, or Local bus data transfer is performed.

Chapter 3 Understanding the HP E1429 Digitizer 143