ICS N4865A, Инструкция по эксплуатации

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A-2
A1
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 specifi cations and the state diagrams for each bus function. The IEEE
Std 488.2 expanded on the original specifi cation and established data for-
mats, 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 manu-
facturers can be controlled by the same program.
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 fi ve lines
control Bus activity.
Two types of messages are transferred over the bus:
Interface messages - for bus management
Device-dependent messages - for device control and data
transfer
Devices connected to the bus may act as talkers, listeners, controllers, or
combinations of the three functions, depending upon their internal capability.
The system controller is a controller that becomes active at power turn-on.
It is the Bus manager and the initial controller-in-charge.