User Manual

2400 Series SourceMeter
®
User’s Manual IEEE-488 Bus Overview D-5
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 man-
agement. These lines are used to send the uniline commands.
ATN (Attention) — The ATN line is one of the more important management lines.
The state of this line determines how information on the data bus is to be inter-
preted.
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.
Handshake lines
The bus handshake lines operate in an interlocked sequence. This method
ensures reliable data transmission regardless of the transfer rate. Generally, data
transfer will occur at a rate determined by the slowest active device on the bus.
One of the three handshake lines is controlled by the source (the talker sending
information), while the remaining two lines are controlled by accepting devices
(the listener or listeners receiving the information). The three handshake lines are: