Valhalla 2300, Operation Manual

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flexibility between independently
manufactured products. The IEEE-488
(1978) standard defines the following:
Electrical characteristics - interface circuit
parameters, electrical signal levels, loading
requirements and grounding requirements.
Mechanical characteristics - connector type,
contact assignments and cable assembly.
Functional characteristics - the complete
repertoire and precise definition of each of the
signal lines, the protocol and timing
relationships and the mandatory responses for
universal (device independent) messages.
The IEEE-488 (1978) standard does
not
define the following:
The way in which device dependent messages
will be interpreted by the receiving device,
leaving these up to the manufacturer to define.
These are defined for the 2300 in Section 7-7.
Maximum amount of time for a full
handshake of data to occur ensuring
compatibility with the slowest device on the
bus (it does define the minimums, however).
7-3-2. IEEE-488 Defined Parameters
The IEEE-488 standard defines a bi-
directional bus carrying bit-parallel, byte-
serial data. The most basic of its definitions
are as follows:
All bus data is digital.
A maximum of 15 devices may be
interconnected on a single bus.
The total length of the bus cabling may not
exceed 20 meters, with a maximum
interconnection cable length of 4 meters.
The maximum data transmission rate is 1
megabyte per second.
Of all the devices on the bus only one may be
the controller at any time. The controller
exercises control over all other devices on the
bus. The other devices may be listeners (only
able to receive data), talkers (only able to
transmit data), or both. The 2300 functions
both as a talker and as a listener. The
controller is the only device capable of
addressing other devices on the bus and
commanding them to talk or listen as required.
Only one device may talk at any one time.
The interconnecting cable shall consist of 16
signal wires and eight ground returns linking
devices into a complete system (the user is
cautioned to be careful of generating ground
loops when interconnecting devices via the
bus). Each cable connector is a plug and
socket combination to permit the "daisy
chaining" of devices.
The 16 signal wires are as follows:
8
data wires (DIO0 through DIO7
inclusive).
5 management wires (ATN, EOI, SRQ, IFC
and REN).
3 handshake wires (DAV, NRFD and
NDAC).
It should be noted that all of these wires use
"inverse logic", i.e. a low voltage level
indicates the "true" state (also called
"asserted") while the high voltage level
indicates the "false" state.
DIO (0 to 7) - These wires are the bi-
directional data bus.
ATN - This wire may be asserted by the
controller to indicate that an address or
command is present on the bus.
EOI - This wire may be asserted by the
controller or the talker. If ATN is also
asserted this indicates that the
controller is polling devices. If ATN
is false, EOI may be asserted by a