HP 5300A - Page 26

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Model 5300A ,
Theory of Operation
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GATES
BINARY CODED OIGIT
SELECT CODE
will set all outputs high which allows other data from
the plug-on to be inserted in place of the counter data.
If no other data is presented, the display remains
blank. In normal operation, the digit select lines X,
Y, and Z are driven by the digit address lines X, Y, and
Z from the display scanner. This multiplexes the six
decades of information into the six digit positions of
the display. When a count of 90,000 has been re-
gistered in the counter (decades 0 to 4), the output
labeled “9” goes low. This signal is used during auto-
ranging, to register a reading of 9% or greater of full
scale.
4-38. A1U4 TIME BASE
CAUTION
This time base is a large-scale MOS integrated
circuit. Its inputs are susceptible to damage by
high voitages and static charges. Particular
care should be exercised when servicing this
circuit or handling it under conditions where
static charges can build up.
4-39. The A1U4 Time Base is a large scale integrated
circuit containing eight decade-divider elements.
Figure 4-8 shows a basic block diagram. It accepts a
maximum input frequency of 10 MHz which gives an
output of one pulse every 10 seconds from the last
decade-divider. The outputs of all decade dividers are
multiplexed into a single time-base output line at
Al1U4(11). The number of stages used to divide the
input signal is determined by a 3-bit binary-coded
select code (pins 7, 8, and 9). Division factors of 10
4-8
4- LINE
Figure 4-7. A1U3 6-Decade Counter Block Diagram
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OVERFLOW
GATES
BINARY CODES
OATA LINES
POSITIVE LOGIC
through 108 can be selected. The first decade stage
may be bypassed by a second input whose maximum
frequency is 1 MHz. This input can be divided by
scaling factors of 1 through 107. The precision timing
and auto-ranging required for frequency and period
average measurements is provided by the LOG output
at pin 1. During the first 10 seconds of a frequency
measurement following reset, this output provides
only 9 pulses. The first pulse triggers the gate open-
ing at time 0, thereafter pulses are obtained at 1,
10, and 100 psec, 1, 10, and 100 msec, 1 sec, and 10 sec.
During auto-ranging, one of these pulses is auto-
matically selected to trigger the gate closing. After
the measurement is in progress, each pulse is
precisely referenced to the Start Pulse at Time 0,
which enables the Stop Pulse to be selected. The time
base can be cleared to zero by a positive reset pulse
at pin 14.
TIME BASE CODE/U4
GATE TIME
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