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REN Programming
Example-The
REN line is set low
(true) by the HP-85 when the following line is entered into the
HP-85.
REMOTE 718 (END LINE)
When the END LINE key is pressed the Model 706 is placed in
the remote and the front panel REMOTE LED is turned on.
3. IFC (Interface Clear)-The
IFC command is sent by the
controller to set the Model 706 to the talk and listen idle
states. The instrument responds to the IFC command by
turning off the front panel TALK or LISTEN LEDs if the in-
_ strument was previously in one of those modes. To send
the IFC command, the controller only has to set the IFC
line true.
IFC Programming
Example-Before
demonstrating
the
IFC command, turn on the front panel REMOTE and TALK
LEDs by entering the following statements into the HP-85.
REMOTE 718 (END LINE)
ENTER 718;AS (END LINE)
The front panel TALK and REMOTE LEDs should now be on.
The IFC command may now be sent by entering the follow-
ing statement into the HP-85.
ABORT10 7 (END LINE)
CLEAR 7 (END LINE)
After the END LINE key is pressed, the TALK LED turns off,
indicating the Model 706 is in the talk idle state. Note that the
remote mode is not cancelled.
4. EOI (End Or Identify)-The
EOI command is used to iden-
tify the last byte of a multi-byte transfer sequence.
5. SRQ (Service Request)-The
SRQ line is set low (true) by
a device when it requires service. SRQ can be identified by
reading the status word.
complete handshake sequence is shown in Figure 3-2. This
sequence handles information one byte at a time.
Once the data is on the bus, the source checks to see that
NRFD is high. At the same time NDAC should be low from
the previous byte transfer. Once the NRFD and NDAC lines
are properly set, the source sets the DAV line low. The NRFD
line goes low; the NDAC line then goes high once all the
devices on the bus have accepted the data. Each device
releases the NDAC line at its own rate, but the NDAC line will
not go high until the slowest device on the bus has accepted
the data.
After the NDAC line goes high, the source sets the DAV line
high indicating that the data is no longer valid. At this point,
the NF)AC line goes low. The NRFD line is released by each
device on the bus but does not go high until the slowest
device on the bus has released the line. The bus is now set to
repeat the sequence with the next data byte.
The sequence just described is used to transfer both data and
multi-line commands. The state of the ATN lines determines
whether the data bus contains data or commands.
DATA
DAV
SOURCE
I
1
NRFD
I
I
I
NDAC
I
I
I
ACCEPTOR
I
I
I
DATA
DATA
TRANSFER
TRANSFER
BEGINS
ENDS
Figure 3-2. Handshake
Sequence
3.2.2 Handshake
Lines
3.2.3 Data Lines
The handshake group consists of three handshake lines
The IEEE-488 bus uses eight data lines that transfer data one
which operate in an interlocked sequence. The interlocked
byte at a time. DlOl (Data Input/Output
1) through
Dl08,
sequence ensures reliable data transfer regardless of the
(Data Input/Output
8) are the eight data lines used to
transfer sequence. The slowest device on the bus usually
transmit
both data and multiline
commands,and
are bi-
determines the rate of transfer.
directional. The data lines operate with low true logic.
The three handshake lines are:
3.3 SYSTEM SET UP PROCEDURE
1. DAV (Date Valid)
2. NRFD (Not Ready For Data)
3. NDAC (Not Data Accepted)
There are two primary set up steps that prepare the system
for operation. The two steps are as follows:
1. Bus Connections-The
Model 706 is connected to the
bus via the rear panel connector. It is a standard IEEE bus
connector. Maximum cable length for any device on the
bus is 20 meters. The Keithley Models 70083 and 70086
The DAV line is controlled by the source. The NRFD and
NDAC lines are controlled
by the accepting devices. The
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