A-2
A
A1
IEEE 488 BUS DESCRIPTION (IEEE 488.1, IEEE
488.2, SCPI)
The IEEE Std 488 Bus is a convenient means of connecting instruments
and computers together to form a test system or to transfer data
between two computers. The IEEE Std 488.1 covers the electrical and
mechanical bus specifications and the state diagrams for each bus
function. The IEEE Std 488.2 expanded on the original specification
and established data formats, common commands for each 488.2
device and controller protocols. The SCPI standard developed a tree
like series of standard commands for programmable instruments so
that similar instruments by different manufacturers can be controlled
by the same program.
The 488-PC2 card provides an IEEE 488 Interface for any IBM PC
computer or compatible ISA bus clone. When used as a bus controller,
the 488-PC2 drivers, driver libraries and windows DDL make the
488-PC2 operate as a 488.2 compatible controller. The controller
protocols are built in to the PC2 drivers. All IEEE 488.2 common
commands, queries and SCPI commands are placed in the output
command string by the user and are not part of the PC2 driver
software.
A1.1
IEEE 488.1 Bus
The IEEE Std 488 Bus, or GPIB as it is commonly referred to,
provides a means of transferring data and commands between devices.
The physical portion of the bus is governed by IEEE -Std 488.1 - 1978.
The interface functions for each device are contained within that
device itself, so only passive cabling is needed to interconnect the
devices. The cables connect all instruments, controllers and other
components of the system in parallel to the signal line as shown in
Figure A-1. Eight of the lines (DIO1-DIO8) are reserved for the
transfer of data and other messages in a byte-serial, bit-parallel
manner. Data and message transfer is asynchronous, coordinated by
the three handshake lines (DAV, NRFD, NDAC). The other five lines
control Bus activity.
