Tabor 8020, Руководство пользователя

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an external device depending on the direction of
data transfer. The following is descriptions of each
command.
REN - (Remote Enable) - The remote enable
command is sent to the Model 8020 by the controller
to set the instrument up for remote operation. Gen-
erally, this should be done before attempting to
program the instrument over the bus. The Model
8020 will indicate that it is in the remote mode by
illuminating its front panel REM indicator. To place
the Model 8020 in the remote mode, the controller
must perform the following steps:
1. Set the REN line true.
2. Address the Model 8020 to listen.
NOTE
Setting REN true without addressing
will not cause the REM indicator to
turn on; however, once REN is true,
the REM light will turn on the next
time an address command is re-
ceived.
EOI (End Or Identify) - The EOI command is
used to positively identify the last byte in a multi-byte
transfer sequence. This allows variable length data
words to be transmitted easily.
IFC (Interface Clear) - The IFC command is sent
to clear the bus and set hand shake lines to a
known state. Although device configurations differ,
the IFC command usually places instruments in the
talk and listen idle states.
ATN (Attention) - The controller sends ATN while
transmitting addresses or multiline commands. De-
vice-dependent commands are sent with the ATN
line high (false).
SRQ (Service Request) - The SRQ command is
asserted by an external device when it requires
service from the controller. If more than one device
is present, a serial polling sequence, as described
in paragraph 4-8-2, must be used to determine which
has requested service.
4-8-2. Universal Multiline Commands
Universal commands are multiline commands that
require no addressing. All instrumentation equipped
to implement the command will do so simultaneously
when the command is transmitted over the bus. As
with all multiline commands, the universal commands
are sent over the data lines with ATN set low:
LLO (Local Lockout) - The LLO command is sent
by the controller to remove the Model 8020 from
the local operating mode. Once the unit receives
the LLO command, all its front panel controls (except
Power) will be inoperative.
NOTE
The REN bus line must be true before
the instrument will respond to an LLO
command.
To lock out the front panel controls of the Model
8020, the controller must perform the following steps:
1. Set ATN true.
2. Send the LLO command to the instrument.
DCL (Device Clear) - The DCL command may
be used to clear the Model 8020, setting it to a
known state. Note that all devices on the bus
equipped to respond to a DCL will do so simulta-
neously. When the Model 8020 receives a DCL
command, it will return to the default conditions listed
in Table 4-4. Factory pre-selected parameters are
listed in Table 3-1. To send a DCL command the
controller must perform the following steps:
1. Set ATN true.
2. Place the DCL command on the bus.
SPE (Serial Poll Enable) - The serial polling
sequence is used to obtain the Model 8020 status
byte. Usually, the serial polling sequence is used to
determine which of several devices has requested
service over the SRQ line. However, the serial polling
sequence may be used at any time to obtain the
status byte from the Model 8020. For more information
on status byte format, refer to paragraph 4-14. The
serial polling sequence is conducted as follows:
1. The controller sets the ATN line true.
2. The SPE (Serial Poll Enable) command is
placed on the bus by the controller.
3. The Model 8020 is addressed to talk.
4. The controller sets ATN false.
5. The Model 8020 then places its status byte
on the bus to be read by the controller.
6. The controller then sets the ATN line low and
places SPD (Serial Poll Disable) on the bus to end
the serial polling sequence.
Steps 3 trough 5 may be repeated for other
instruments on the bus by using the correct talk
address for each instrument. ATN must be true when
Model 8020 IEEE-488.2 Operation
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