Section 5
OM6530-C1-00
19 November, 2019
5-2
This manual assumes that the user is familiar with the basics of the IEEE-488 interface bus.
The IEEE-488 interfacing standard applies to the interface of instrumentation systems or portions
of them, in which the:
1.
Data exchanged among the interconnected apparatus is digital.
2.
Number of devices that may be interconnected by one contiguous bus does not exceed 15.
3.
Total transmission path length over interconnecting cables does not exceed the lesser of
either 20 meters or 2 meters times the number of devices on the bus.
4.
Data rate across the interface on any signal line does not exceed 1 megabit per second.
5.2.1.
CONTROLLER
There can be only one designated controller in charge on the IEEE-488 bus. This device
exercises overall bus control and is capable of both receiving and sending data. The rest
of the devices can be designated as listener, talker or talker/listener.
The controller can address other devices and command them to listen, address one device
to talk and wait till the data is sent. The controller sets data routes but it need not take part
in the data interchange.
All controller query and command sequences should be terminated with the line-feed
character (0x0A) and/or optionally; the controller should assert the EOI data byte control
signal.
5.2.2.
IEEE-488 RESPONSES
The reply to any IEEE-488 query command will be a sequence of ASCII characters
followed by a line-feed character (0x0A). The line-feed character may also be expressed
as 0A
16
or 10
10
or 12
8
or Ctrl-J. Throughout this manual we will use the "C"
programming language notation for expressing numbers in base 16, specifically 0x0A
indicates that 0A is to be interpreted in base 16 (hex).
5.2.3.
INTERCONNECTING CABLE AND IEEE-488 CONNECTOR
The interconnecting cable of IEEE-488 1978 consists of 24 conductors, 16 conductors are
for carrying signals and 8 for grounding. An individual cable assembly may be up to 4
meters long and should have both a plug and a receptacle connector type at each end of
the cable. Each connector assembly is fitted with a pair of captive locking screws.
5.2.4.
TYPICAL SYSTEM
Data Input/Output Lines - The 8 data I/O lines form the data bus over which data between
the various devices is transmitted under the supervision of the controller. The message
bytes are carried on Data I/O signal lines in a bit parallel byte serial form, asynchronously
and generally in a bi-directional manner.
Handshake or Data Byte Control - the three interface signals are used to effect the
transfer of each byte of data on the DIO signal lines from a talker or controller or one or
more listeners.
