Bus Lines; Data Lines; Bus Management Lines - Keithley 2016 User Manual

D-6 IEEE-488 Bus Overview

Bus lines

The signal lines on the IEEE-488 bus are grouped into three different categories: data lines,
management lines, and handshake lines. The data lines handle bus data and commands, while
the management and handshake lines ensure that proper data transfer and operation takes place.
Each bus line is active low, with approximately zero volts representing a logic 1 (true). The
following paragraphs describe the operation of these lines.

Data lines

The IEEE-488 bus uses eight data lines that transfer data one byte at a time. DIO1 (Data
Input/Output) through DIO8 (Data Input/Output) are the eight data lines used to transmit both
data and multiline commands and are bidirectional. The data lines operate with low true logic.

Bus management lines

The five bus management lines help to ensure proper interface control and management.
These lines are used to send the uniline commands.
ATN (Attention) — The ATN line is one of the more important management lines in that the
state of this line determines how information on the data bus is to be interpreted.
IFC (Interface Clear) — As the name implies, the IFC line controls clearing of instruments
from the bus.
REN (Remote Enable) —The REN line is used to place the instrument on the bus in the
remote mode.
EOI (End or Identify) — The EOI is usually used to mark the end of a multi-byte data transfer
sequence.
SRQ (Service Request) — This line is used by devices when they require service from the
controller.