National Instruments GPIB-140A User Manual - page 16
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Configuring and Using
Your Hardware
This chapter describes how to configure and use your GPIB-140A or GPIB-140A/2 system.
Data Transfer Modes
The GPIB extender has two data transfer modes—unbuffered mode and buffered mode. The data
transfer mode determines how data is transmitted across the extension.
Selecting a Data Transfer Mode
To select a data transfer mode, refer to the following descriptions of each mode.
Unbuffered Mode
In unbuffered mode, each data byte is transmitted using the GPIB double-interlocked
handshaking protocol. For long data streams, transfers are slower than transfers using buffered
mode. However, the GPIB extension is transparent in unbuffered mode.
Buffered Mode
In buffered mode, the GPIB extenders use FIFO (first-in-first-out) buffers to buffer data between
the remote and local units. For long data streams, the data throughput is much higher than with
unbuffered mode.
However, a few applications may not operate properly in buffered mode. For example, a GPIB
device on the local side of the extension is addressed to talk, another device on the remote side
is addressed to listen. When the Talker sources data bytes, the GPIB extenders accept the data
bytes and store them in a FIFO buffer. At the same time, the GPIB extenders read data from the
FIFO buffer and source data bytes to the Listener. If the FIFO buffer contains data, the number
of bytes sourced by the Talker differs from the number of bytes accepted by the Listener.
GPIB command bytes are not stored in the FIFO buffers; they are transmitted using the GPIB
double-interlocked handshaking protocol.