Measurement-computing Serial488A Instrukcja Użytkownika Pobierz pdf (Strona 64)

5.5

5.4.2 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

5.4.3 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.

5.4.4 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

5.4.5 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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