Section 5
5-2
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. Data routes are set by the controller 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 to terminate the query command sequence.
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 control-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. The individual cable assembly could be up to 4
metres long. The cable should be double shielded and should have both a shielded plug and
a receptacle connector type at each end of the cable. Guildline Part Number 996-23006 is a
suitable IEEE-488 cable assembly of length 2 metres. 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 bidirectional 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.
To Next Page
Loading...