Measurement-computing Digital488 Manual de usuario descargar pdf (Pagina 64)

Section 4 IEEE 488 Primer

4.4

4.3 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).

4.4 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, i.e. a low voltage represents a logic "1" (asserted), and a high voltage

represents a logic "0" (unasserted).

4.4.1 Attention (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 is not, then that information is to be interpreted as data for

the

Active Listener

s. The

Active Controller

is the only bus device that has control

of this line.

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