Black Box IC095A, Руководство пользователя

Страница: 23 / 35

20
IEEE 488 BUS EXTENDER AND IEEE 488 FIBER BUS EXTENDER
5.3 Send It to My Address
In the previous discussion, the terms Addressed to Talk and Addressed to Listen
were used. These terms require some clarification.
The IEEE 488 standard permits up to 15 devices to be configured within one
system. Each of these devices must have a unique address to avoid confusion. In a
similar fashion, every building in town has a unique address to prevent one home
from receiving another home’s mail. Exactly how each device’s address is set is
specific to the product’s manufacturer. Some are set by DIP switches in hardware,
others by software. Consult the manufacturer’s instructions to determine how to
set the address.
Addresses are sent with universal (multiline) commands from the Active
Controller. These commands include My Listen Address (MLA), My Talk Address
(MTA), Talk Address Group (TAG), and Listen Address Group (LAG).
5.4 Bus Management Lines
Five hardware lines on the GPIB are used for bus management. Signals on these
lines are often referred to as uniline (single-line) commands. The signals are active
low—that is, a low voltage represents a logic “1” (asserted), and a high voltage
represents a logic “0” (unasserted).
5.4.1 A
TTENTION
(ATN)
ATN is one of the most important lines for bus management. If Attention is
asserted, then the information contained on the data lines is to be interpreted as a
multiline command. If it isn’t, then that information is to be interpreted as data for
the Active Listeners. The Active Controller is the only bus device that has control
of this line.
5.4.2 I
NTERFACE
C
LEAR
(IFC)
The IFC line is used only by the System Controller. It is used to place all bus
devices in a known state. Although device configurations vary, the IFC command
usually places the devices in the Talk and Listen Idle states (neither Active Talker
nor Active Listener).