Agilent Technologies HP 82335, Install Manual, Page: 42 / 54

HP·IB Fundamentals
Controllers, Talkers, and Listeners
designated as the system controller. This controUer is the only one that can
control lhe
IFe
and REN lines.
Control is passed to another controller by addressing it as a talker and
commanding it to "take control" (TCT).
Talker
In
each system, there can be at most one device addressed as talker al any
given time. A device becomes addressed as talker by receiving its talk
address from the active controller. Each device on the bus must have a
unique bus address. This address is usually set al the manufacturing site, but
it may be set by switches on the instrument.
The addresses are in the range 0 to 30. A talk address is formed by adding
the primary bus address to the talk address base value of 64 and transmitting
that value across the data lines while ATN is asserted. For example, talk
address 9 would be formed by asserting ATN and transmitting a byte whose
value is 73 (64 + 9
=
73, ASCII character "I").
Listener
Listen addresses are formed in a similar manner to talk addresses. except
that listen addresses use a base of 32. For example, listen address
9 is sent as
value
41
transmitted with ATN true (32
+
9
=
41,
ASCfI character ")" ).
Multiple devices may be addressed to listen at any time, and dala bytes will
be received by all listeners in parallel. However, most devices cannot be
addressed to both talk and listen at the same time. (See Table A·3 on
page 38 for ASCII Codes.)
Extended Addressing
The descriptions of talk address and listen address refer to a device's primary
address. Some devices also have extended talker or extended listener
capabilities, sometimes used as secondary addresses or as device-dependent
commands. With extended addressing, talk and listen addresses are
represented by two command bytes. The first byte is the primary talk or
listen address as previously described. The second byte is a secondary
address command.
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