HP 5384A Operating And Service Manual page 133

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8-204. To convert the count in the interpolator to
real nanoseconds, the MRC provides two calibration
pulses; a short calibration pulse of 100 ns and a long
calibration pulse of 200 ns. By inputting each of these
known length pulses into the same integrator and
noting the number of counts produced, a mathe-
matical proportion is established, with which the true
time for any pulse length can be interpolated. For
example, if the short (100 ns) calibration pulse
produced 200 counts, and the long (200 ns) calibration
pulse produced 400 counts, a pulse of 1SO ns would
produce 300 counts. Inversely, if 300 was the number
of counts accumulated during the interpolator pulse
integrator cycle, then the error factor would be 1SO
ns. Refer to Figure 8-39.
8-20S. The final equation for determining the actual
gate time is:
MEASUREMENT TIME = (counts in T-register) X 100 ns
Count X-Count S
+ - - - - - - - - - X 100 ns
Count L-Count S
(for the Start Interpolator)
Count X-Count S
_ _ _ _ _ _ _ _ _ X100ns
Count L-Count S
(for the Stop Interpolator)
where:
Count X= effective counts from interpolation
pulse
CountS= effective counts from short cali-
bration pulse
Count L = effective counts from long cali-
bration pulse
For example, given the following values:
Count in MRC T register
=
10
Count from Start Interpolator
Count from Stop Interpolator
Count from short calibration pulse
Count from long calibration pulse
= 100 (+256)
= 230
GATE TIME
=(10X100ns)+
356-200
406-200
X100ns-
= 200
= 150 (+256)
230-200
406-200
X100ns
=1000 ns +75.7 ns -14.6 ns =1061.1 ns
8-206. The general measurement program routing is
to make a measurement, read the MRC registers, read
the interpolator counters, perform the calculations,
and display the results. In between measurements,
the MRC registers and the interpolator counters are
reset.
HP S384A and HP S38SA
Service
ACCUMULATED
COUNTS
400
COUNTSr--------~~
300
COUNTS
200
COUNTS
r-----,(
100 200
SHORT LONG
PULSE PULSE
150 ns
INTERPOLATOR COUNTS
TIME
NANOSECONDS
Figure
8-39.
Short and Long Calibration Pulses Example
8-207. HP-18
8-208. The HP-IB, AS board of the HP S384A and HP
S38SA counters (figure 8-52) consists of two line
transceivers (U1 and U2), a quad nand gate (U4) and a
3870 microcomputer (US), and a few other discrete
components.
8-209. The line transceiver ICs are bidirectional
buffer amplifiers. Each transceiver buffers 8 of the 16
data lines used in HP-IB. (Eight lines are used as a data
bus for information transfer, S lines for general bus
management, and three lines for the handshake
sequence.) Direction of data flow is controlled by
disabling the undesired direction buffer. The buffers
are controlled by TTL logic level inputs to U1(4, 8, 11,
17) and U2(17). A logic high on these pins causes data
to be transmitted onto the interface bus. A logic low
causes data to be received from the interface bus. The
transceivers are switched by U3.
8-210. U3 also pulls the NDAC line low to start the
handshake for the information which is sent by the
controller with the line true (0).
8-211. The latch (U4) receives short pulses from the
Remote Enable (REN) and the Interface Clear (IFC)
lines and holds the information until the software in
the microcomputer reads them.
8-27