Measurement-computing Isolator488 Instrukcja Użytkownika Pobierz pdf (Strona 25)

Section 3 IEEE 488 Primer

3-4

3.3 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).

3.4 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).

3.4.1 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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