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Chapter 4
Theory of Operation
Message Interpreter Layer
The Message Interpreter Layer handles the handshake between the GPIB extender and other
devices on the GPIB. At the same time, the layer monitors the activities that occur on the GPIB,
translates them into equivalent local and remote GPIB messages, and sends these messages to
the Packet Translation Layer.
Packet Translation Layer
The Packet Translation Layer converts the messages that it receives to packets and sends them
to the Link Management Layer. It can also receive packets from the Link Management Layer
and convert them back to local or remote GPIB messages.
Link Management Layer
The Link Management Layer receives packets from the Packet Translation Layer. It sends the
packets to the Parallel-to-Serial Conversion Layer and it stores them in a local buffer. If a
transmission error occurs, the Link Management Layer can re-send the packets from this local
buffer. The Link Management Layer also receives packets from the Parallel-to-Serial
Conversion Layer and checks the packets for transmission errors. If the Link Management Layer
does not detect an error, it sends the packets to the Packet Translation Layer. However, if it
detects a transmission error, the it re-transmits the packets.
Parallel-to-Serial Conversion Layer
The Parallel-to-Serial Conversion Layer accepts packets from the Link Management Layer,
converts them into serial data, and sends the data to the Physical Layer. It also extracts serial bits
from the Physical Layer, reconstructs them back into packets, and sends them to the Link
Management Layer.
Physical Layer
The Physical Layer transmits and receives serial data over the fiber-optic link.