Measurement-computing Isolator488 Instrukcja Użytkownika Pobierz pdf (Strona 26)

Section 3 IEEE 488 Primer

3-5

3.4.2 Interface Clear (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

3.4.3 Remote Enable (REN)

When the

System

Controller

sends the

REN

command, bus

devices will respond to remote operation. Generally, the

REN

command

should be issued before any bus programming is attempted. Only the

System

Controller

has control of the

Remote

Enable

line.

3.4.4 End or Identify (EOI)

The

EOI

line is used to signal the last byte of a multibyte data

transfer. The device that is sending the data asserts

EOI

during the

transfer of the last data byte. The

EOI

signal is not always necessary as

the end of the data may be indicated by some special character such as

carriage return.

The

Active

Controller

also uses

EOI

to perform a

Parallel

Poll

simultaneously asserting

EOI

and

ATN

3.4.5 Service Request (SRQ)

When a device desires the immediate attention of the

Active

Controller

it asserts

SRQ

. It is then the Controller's responsibility to

determine which device requested service. This is accomplished with a

Serial Poll

or a

Parallel Poll

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