HP 8920A, User Manual

Page: 466 / 658

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S:\HP892XX\USRGUIDE\manual\radscrn.fb
Chapter 16, Radio Interface Screen
Using the Radio Interface (Manual Operation)
Outputting Data
Outputting data is accomplished by entering the appropriate hex value in the
Output Data
field, and then selecting the
Send Data
field.
The output data value can be incremented or decremented by turning the cursor
control knob with the
Output Data
field highlighted.
The output data lines are implemented by open-collector output voltage
comparators. Sending a logic 0 causes active pull-down through a transistor in the
voltage comparator. Sending a logic 1 causes passive pull-up through a pull-up
resistor.
Variations in the Logic Voltage can be used to provide logic levels compatible
with the radio-under-test. See
"Setting the Radio Interface’s Logic Level" on page
463
.
The data transfer rate for data output is primarily determined by the speed of the
IBASIC or external program, not the ability of the Test Set’s internal CPU to
access and output the data on the parallel lines, or the output loading capacitance.
(If loading capacitance is below 158 pF, the Test Set’s CPU can send data at about
200 Kb/s. The time for a program line to execute is typically greater than this).
The Parallel Strobe Out, pin 13, can be used to signal when output data has been
clocked onto the parallel data bus. The front-panel RADIO INTERFACE screen
allows the choice of strobe polarity through the
Strobe Pol
field. As with the
parallel data outputs, the Parallel Strobe Out logic threshold is determined by the
Logic Voltage. Although the edges of Parallel Strobe Out and data output occur at
approximately the same time, an external device should latch on the Strobe Pol
trailing edge, or better yet, the Strobe Pol level. This will allow sufficient time for
output data to settle. Refer to
figure 119 on page 467