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Theory of Operation
Chapter 4
GPIB-130 User Manual
4-2
© National Instruments Corporation
When the GPIB-130s leave the PON state, the Link LED turns on and the extension system
becomes operational.
System Controller Detection
The System Controller Detection circuitry locates the GPIB System Controller if one is present
in the system. The System Controller may be on either the local side or the remote side of the
GPIB-130 extension.
The ANSI/IEEE Standard 488.1-1987 restricts a GPIB system to having only one System
Controller. However, the GPIB-130s work in systems that have more than one System
Controller. A GPIB device should assert the Interface Clear (IFC) message to become the
System Controller.
Controller-In-Charge Detection
The Controller-In-Charge (CIC) Detection circuitry locates the GPIB Controller-In-Charge if one
is present in the system. The GPIB Controllers may be on the local side, the remote side, or both
sides of the GPIB-130 extension. Devices on one side of the extension system may pass control
or take control from devices on the remote side of the extension.
Source Handshake Detection
The Source Handshake Detection circuitry locates the device sourcing GPIB command or data
bytes. Command bytes may be sourced by the CIC; data bytes may be sourced by the addressed
GPIB Talker.
One or more devices in the system may be addressed as GPIB Listeners. Listeners may be on
the same side, the opposite side, or both sides of the GPIB-130 extension.
Parallel Poll Detection
The Parallel Poll Detection circuitry determines when the CIC is conducting a parallel poll. The
GPIB-130 responds to parallel polls according to the Parallel Poll Response (PPR) mode chosen
by the position of switch 2 (see the Parallel Poll Response (PPR) Modes section in Chapter 3).
Devices on both sides of the extension may respond to parallel polls.
FIFO Controller
The FIFO Controller manages data flow into and out of the GPIB-130's FIFO. For long data
streams, you can obtain a much higher data throughput with Buffered mode than with
Unbuffered mode. The FIFO Controller remains inactive unless a device is sourcing data bytes
and the GPIB-130 is configured to be in Buffered mode. See the Operating Modes section in
Chapter 3.
Each GPIB-130 contains a FIFO and the FIFO Controller circuitry, so GPIB Talkers on both
sides of the extension can use Buffered mode.