HP 53131A/132A 225 MHz Programming Manual page 16

Chapter 1 Before You Start ...
Differences Between Prior and Current Revisions of the HP
53131A/132A
Measurements
If your Counter contains other than the current firmware revision, the following
measurement capabilities are different:
Ratio channel selections Ratio 2 to 1 and Ratio 3 to 1
(for those counters equipped with Channel 3) are not available.
Ratio "AUTO-armed" does not automatically extends gate to capture
sufficient edges.
If Channel 1 input frequency is less than approximately 10 Hz, the Ratio
gate time is not extended to capture sufficient Channel 1 edges to produce
a valid measurement. Default gate time is 100 msec, which is not long
enough to capture two edges on a low-frequency signal. The user is
required to extend the gate by switching to TIME arming, and selecting a
gate time appropriately long.
Sensitivity for firmware revision below does not have adjusted controls to
LO and MED sensitivity.
In some Counters that contained firmware revision 3317,
LO sensitivity fails to correctly count very high frequency signals.
Statistics
If your Counter contains other than the current firmware revision s, single-shot
statistics are not available using the ON SINGLE: menu item found in the
Statistics menu (use Stats key).
HP-IB Commands
[:SENSe]:EVENt[1|2}:HYSTeresis:RELative
If your Counter contains firmware revision s 3402 and below, the input hysteresis
command and query does not operate in the conventional way. That is,
[:SENSe]:EVENt[1|2]:HYSTeresis:RELative sets high sensitivity when the
parameter is MINimum or 0 percent, and sets low sensitivity when the parameter
is MAXimum or 100 percent.
In the prior firmware revisions (3317, 3335, or 3402), MINimum or 0 percent
corresponded to low sensitivity, and MAXimum or 100 percent corresponded to
high sensitivity.
1-4 Programming Guide