HP 8920A, User Manual

Page: 463 / 658

463
Chapter 16, Radio Interface Screen
Using the Radio Interface (Manual Operation)
Using the Radio Interface (Manual Operation)
CAUTION: Do not connect a voltage source in excess of
−
0.3 V (for example,
−
0.4 V) to any Parallel Data
pin. Also, do not connect a voltage source that exceeds 5.7 V, unless the logic voltage has been
set to a level other than the default. If the logic voltage has been set to some value other than the
default of 5.1 V, the maximum voltage that can be applied is the logic voltage plus 0.6 V. Refer
to
"Setting the Radio Interface’s Logic Level" on page 463 .
Setting the Radio Interface’s Logic Level
The logic levels on the parallel data bus are determined by the Logic Voltage. The
two choices for the Logic Voltage are 5.1 V from the default (internal) Logic
Voltage supply, or 5.1 V to 20 V from an external power supply.
The Logic Voltage affects both the input and output logic levels on the Radio
Interface board. When data is output, the logic-high voltage level will be
determined by the Logic Voltage applied through internal 3.16 k-ohm pull-up
resistors. When data is input, the voltage comparator’s reference voltage is
determined by the Logic Voltage applied to a resistive divider. The formulas for
calculating logic levels are shown below. The default values are calculated in the
examples, and if these are not compatible with the device that is sending/receiving
data, connect an external power supply to pin 9. At levels above +5.1 V, the
external power supply will reverse bias a steering diode and “turn off” the default
Logic Voltage. See
figure 118 on page 464
.