HP 3335A - HP-IB Communication Protocols; HP-IB Bus Messages; HP-IB Remote Operation Control

Section III
FALSE
DIOI-DIO8
TRUE
FALSE
DAV
TRUE
FALSE
NRFOD
TRUE
FALSE
NDAC
TRUE
(A) and (B)
NOTE: Events
O through
o |©
Note- HP-IB logic is iow true
Comment
The interval between A and
B indicates when one byte of
information is on the data lines,
DIOt through DIO8.
NOTE
For the remainder of this explana-}
tion, the term “data” refers to
one byte of information fone
seven-bit ASCH character).
Listener indicates he is ready to
receive data.
Source recognizes listener is ready
for data, places a new character
on theDIO lines and indicates to
the listener the data on the DIO
lines is valid.
Listener recognizes the data is
valid and indicates to the source
he is not ready for any new
data. The listener accepts the data
on the DIO fines to store internal-
ly after NRFD goes true.
The listener indicates to the
source that he has stored internal-
ly the data on the DIO lines.
When the data is stored, internal
processing begins.
Source recognizes that the listener
has accepted and stored internally
the data on the DIO lines. Source
removes the data valid indication
by setting DAV false in prepara-
tion for placing the next byte of
information on the DIO Hnes.
Listener recognizes that the
source has acknowledged its
acceptance of the data and
removes the data accepted indi-
cation. Listener continues to
process the internally stored data.
When the listener completes pro-
cessing the internally stored data,
the, listener sets NRFD false
which indicates he jis ready to
receive the next byte of informa-
tion,
Q) must occur for each byte of
information iransferred between devices on the HP-iB.
Figure 3-2, HP-IB “Handshake” Sequence of Events.
3-12
Model 3335A
Table 3-3, Bus Messages.
Device Data Transfers device-dependent infor-
Cammunications mation from one device to one or
more devices on the Bus.
Trigger Causes a group of selected devices
to simultaneousty initiate a set of
device-dependent actions.
Clear Causes an instrument to be set to
a predefined state {a certain
range, function, etc.).
Remote Permits selected devices to be set
to remote operation, allowing
parameters and device characteris-
Device tics to be controlled by Bus
Control Messages.
Local Causes selected devices to return
to local (front panel} operation.
Local Disables local (front panel)
Lockout controls of selected devices.
Clear Returns all devices to locat (fromt
Lockout | panel) control and simultaneously
& Local clears the Local Lockout Message.
Require indicates a device's need for inter-
Service action with the controller.
Status Presents status information of a
Byte particular device; one bit indicates
whether or not the device current-
f Interrupt ly requires service, the other 7
and bits (optional) are used to indi-
Device cate the type of service required,
Status
A single bit of device-dependent
status information which may be
logically combined with status bit
information from other devices
by the controller.
Passing
Control
Pass
Control
Passes bus controller responsibili-
ties from the current controller to
a device which can assume the
Bus supervisory role.
Bail Abort
Out
Unconditionaliy terminates Bus
communications and returns con-
trol to the system controller.
3-70. Messages are the means by which devices communi-
cate on the HP—IB. Table 3-3 lists the Bus Messages by Bus
function and provides a description of each.
3-71. HP—iB Remote Operation.
3-72. The HP—IB Remote Enable (REN) line controls the
instrument’s mode of operation, LOCAL or REMOTE.
With no input on the REN line, it is held high by an
internal puilup maintaining the 3335A in the LOCAL mode
of operation. When the 3335A listen address is transmitted,
the REN line is pulled low causing it to go into the remote
control mode. The REN lines does not have internal storage
and must be held in the low state as long as remote opera-
tion is required. Once the 3335A has been put into the