Measurement Computing Extender488 - Manual (Page 24)

Section 3 IEEE 488 Primer
3-4
3.3 SEND IT TO MY ADDRESS
In the previous discussion, the terms Addressed to Talk and Addressed to Listen were u sed.
These terms require some clarification.
The IEEE 488 standard permits up to 15 devices to be configured within one system. Each of these
devices must have a unique address to avoid confusion. In a similar fashion, every building in town has a
unique address to prevent one home from receiving another home's mail. E xactly how eac h device's
address is set is specific to the product's manufacturer. Some are set by DIP switches in hardware, others
by software. Consult the manufacturer's instructions to determine how to set the address.
Addresses are sent with universal (multiline) commands from the Active Controller. Thes e
commands include My Listen Address (MLA), My Talk Address (MTA), Talk Address Group (TAG),
and Listen Address Group (LAG).
3.4 BUS MANAGEMENT LINES
Five hardware lines on the GPIB are us ed for bus management. Signals on these lines are often
referred to as uniline (single line) commands. The signals are active low, i.e . a low v oltage represents a
logic "1" (asserted), and a high voltage represents a logic "0" (unasserted).
3.4.1 Attention (ATN)
ATN is one of the most important lines for bus management. If Attention is asserted, then the
information contained on the data lines is to be interpreted as a multiline command. If it is not, then
that information is to be interpreted as data for the Active Listeners. The Active Controller is the
only bus device that has control of this line.