HP 8920A - Data I;O; Radio Interface Functional Description

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Chapter 16, Radio Interface Screen
Radio Interface Functional Description
Radio Interface Functional Description
Data I/O
The rear-panel connector labeled OPTION INTERFACE is present on Test Sets
with a Radio Interface board. This connector has 16 pins that are used for parallel
data transfer between an external device and the Test Set’s internal CPU.
The Radio Interface board includes 32 voltage comparators used for data input/
output. Sixteen of the comparators have their outputs connected to the Radio
Interface’s 16 parallel data pins, and 16 comparators have their inputs connected
to the Radio Interface’s 16 parallel data pins.
Data transfer is asynchronous, meaning that each block of data is transferred after
a key is pressed on the Test Set’s front panel, or an HP-IB command is sent. Data
transfer is also “half-duplex”, meaning that data input and output cannot occur
simultaneously.
The parallel output data lines are implemented using 16 LM339M open-collector
voltage comparators with pull-up resistors provided on the Radio Interface board.
The Radio Interface provides two methods for determining the logic level for data
output:
1. Use the default (internal) power supply and internal pull-up resistors.
2. Use an external supply voltage connected to the internal pull-up resistors on the Radio
Interface board.
These methods are described in "Setting the Radio Interface’s Logic Level" on page
463
.
The parallel input data lines are implemented using another 16, LM339M, open-
collector voltage comparators. An external supply voltage can be used to provide
the reference voltage to the comparators if the default supply is not compatible
with the external device-under-test.
This procedure is also described in
"Setting the Radio Interface’s Logic Level" on
page 463
.