Bus Line Definitions; Gpib Structure - Wavetek 75 Instruction Manual

CONTROLLER
'ii&NS'.lI-S A h 3 S E C E V E S
D A T A A N 3 M A h A G E S '*E BUS
TALKERILISTENER
TRANSMITS OR
RECEIVES DATA
ONLY RECEIVES DATA
I N T E R F A C E
M A F i A G E M E N T
ONLV T R A N S h l l T S D A T A
A - h
S R O
REFi
Figure 3-7. GPlB Structure
REN
(ATN false) or a command (ATN true).
Whenever ATN is set true, no activity is
allowed on the bus except for controller
originated messages.
The Remote Enable line controls whether
devices on the GPlB are in local or
remote modes. I n the local mode,
devices respond to front panel
commands. In remote mode, the situa-
tion is reversed; GPlB originated com-
mands are obeyed, while front panel
commands are ignored. The Wavetek
Model 75 enters the remote state when
it receives its listen address and REN is
enabled. The Wavetek Model 75 then
stays in the remote mode until the REN
line is put in the local state, aGoTo Local
(GTL)command is received or the LOCAL
front panel soft key is pressed.
DAV, NRFD, These are the "handshake" lines (Data
N DAC Valid, Not Ready For Data and Not Data
Accepted) which regulate the transmis-
sion of information over the lines D101-
D108. For each command or data byte
transferred, a complete handshake cy-
cle occurs. This handshake is designed
to hold up the bus until the slowest device
has accepted the information.
3.27.1
Bus Line Definitions
The 16 negative-true GPlB signal lines are:
Dl01 -Dl08
ATN
REN
DAV
NRFD
N DAC
EOI
SRQ
I FC
Data InlOut Lines
Attention
Remote Enable
Data Valid
Not Ready For Data
Not Data Accepted
End Or Identify
Service Request
Interface Clear
The functions of the GPlB signal lines are:
D l 0 1 -0108 These eight lines (Data InlOut) are used
to send commands from the controller
and to transfer data back and forth
between instruments and the controller.
I FC
ATN The Attention line is operated only by the
activecontroller. It specifieswhether the
information on lines Dl01 -0108 is data
When ATN is false, EOI (End Or Identify)
indicates that the data on lines 0101-
D l 0 8 is the last byte of a data message.
When the Wavetek Model 75 receives a
data byte with EOI true, it automatically
supplies a terminator character follow-
ing the data byte. When the Wavetek
Model 75 transmits the last byte of a
message (which is always a terminator
character) it also sets EOI true.
The Service Request line is used by the
Wavetek Model 75 and other devices on
the bus to signal the controller that they
request attention. Since the SRQ line is
common to all devices, additional tests
must be made to determine which
devices are signaling. The controller per-
forms a Serial Poll to accomplish this.
The Interfaceclear line is asserted by the
system controller to reset the interface
logic in all devices connected to the bus
to a known initial state.
Scans
by
ArtekMedia O 2006