User manual

D-6 IEEE-488 Bus Overview 2400 Series SourceMeter

User’s Manual

DAV (DATA VALID) — The source controls the state of the DAV line to indicate to

any listening devices whether or not data bus information is valid.

NRFD (Not Ready For Data) — The acceptor controls the state of NRFD. It is

used to signal to the transmitting device to hold off the byte transfer sequence

until the accepting device is ready.

NDAC (Not Data Accepted) — NDAC is also controlled by the accepting device.

The state of NDAC tells the source whether or not the device has accepted the

data byte.

Figure D-2

IEEE-488 handshake sequence

Bus commands

The instrument may be given a number of special bus commands through the

IEEE-488 interface. This section briefly describes the purpose of the bus com-

mands which are grouped into the following four categories.

1. Uniline commands — Sent by setting the associated bus lines true. For

example, to assert REN (Remote Enable), the REN line would be set low

(true).

2. Multiline commands — General bus commands which are sent over the

data lines with the ATN line true (low).

3. Common commands — Commands that are common to all devices on the

bus; sent with ATN high (false).

4. SCPI commands — Commands that are particular to each device on the

bus; sent with ATN (false).

These bus commands and their general purpose are summarized in Table D-1.

Data

DAV

Source

Valid

All Ready

Acceptor

NRFD

NDAC

All Accepted

Acceptor