Measurement Computing Serial488/4 - Manual (Page 75)

Section 4 IEEE 488 Primer
4.4
4.3 SEND IT TO MY ADDRESS
In the previous discussion, the terms Addressed to Talk and Addressed to
Listen were used. 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. Exactly how each device's address is set is specific to
the product's manufacturer. Some are set by D IP switches in hardware, others by
software. Consult the manufacturer's instructions to determine how to set the address.
Addresses are sent w ith universal (multiline) commands from the Active
Controller. These commands include My Listen Address (MLA), My Talk
Address (MTA), Talk Address Group (TAG), and Listen Address Group (LAG).
4.4 BUS MANAGEMENT LINES
Five hardware lines on the GPIB are used 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 voltage represents a logic "1" (asserted), and a high voltage represents a
logic "0" (unasserted).
4.4.1 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.