Logic Device Notation Example; 3-State Bidirectional Transceiver - HP 5334B Service Manual

8-66. Logic Device Notation Example
8-67. The various logic symbols are combined to represent more complex devices that perform more difficult
functions. The control block symbol can simplify understanding of many complex devices. An example of such a
device is given here. This example is typical of the symbols used in the schematic diagrams in this manual.
This device is used as an interface between an external controller and the HP-IB microcomputer on the
Data Bus.
In this example, GI controls both EN2 and EN3. The logic level on pin 11 determines whether data is trans-
mitted or received.
With a LOW at G1 (pin 9), the device is enabled for operation. A HIGH at pin 11 sets the device into the
transmit mode and the data on the left-side inputs will pass to the right-side outputs.
A LOW at pin 11 sets the device into the receive mode and the data on the right-side inputs will pass to the
left-side outputs.
A HIGH at G1 disables the device (by driving all inputs and outputs to a high impedance state) preventing
any data transfer.
TRANSMIT
4
RECEIVE
+
Figure
8-4.
3-State Bidirectional Transceiver
HP 5334B
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Service
Manual
8-14