Interface Messages (Ieee-488 Only) - Fluke 5790B Operator's Manual

Interface Messages (IEEE-488 Only)

Interface messages manage traffic on the bus. Device addressing and clearing,
data handshaking, and commands to place status bytes on the bus are all
directed by interface messages. Some of the interface messages occur as state
transitions of dedicated control lines. The rest of the interface messages are sent
over the data lines with the ATN signal true. All device-dependent and common
commands are sent over the data lines with the ATN signal false.
IEEE-488 standards define interface messages. Table 6-4 lists the interface
messages that the Product accepts. Table 6-5 lists the interface messages that
the Product sends. The mnemonics listed in the tables are not sent as literal
statements as commands are. In this way they are different from device-
dependent and common commands.
Interface messages are handled automatically in most cases. For example,
handshake messages DAV, DAC, and RFD automatically occur under the
direction of an instrument interface itself as each byte is sent over the bus.
Table 6-4. Interface Messages Accepted by the Product
Mnemonic Name
ATN Attention
DAC Data Accepted
DAV Data Valid
DCL Device Clear
END End
GTL Go To Local
LLO Local Lockout
IFC Interface Clear
My Listen
MLA
Address
My Talk
MTA
Address
REN Remote Enable
Ready For
RFD
Data
Selected
SDC
Device Clear
Serial Poll
SPD
Disable
Serial Poll
SPE
Enable
UNL Unlisten
UNT Untalk
A control line used to notify all instruments on the bus that the next
data bytes are an interface message. If ATN is low, these data
bytes are interpreted as device-dependent or common commands,
addressed to a specific instrument.
Set the handshake signal line NDAC low.
Asserts the handshake signal line DAV.
Clears the input/output buffers.
A message that is shown when the controller asserts the EOI
signal line before sending a byte.
Transfers control of the Product from one of the remote states to
one of the local states.
Transfers remote/local control of the Product.
A control line that sets the interface to a quiescent state.
Addresses a specified device on the bus as a listener. The
controller sends MLA automatically whenever it directs a device-
dependent or common command to a specified instrument.
Addresses a specific device on the bus as a talker. The controller
sends MTA automatically when it directs a device-dependent or
common command to a specific instrument.
Transfers remote/local control of the Product.
Set the handshake signal line NRFD low.
Identical to DCL, but only operates when the Product is addressed
as a listener.
Cancels a Serial Poll Enable.
Causes the Product to return a Status Byte to the next command
that addresses it as a listener, no matter what the command is.
"Unaddresses" a specific device on the bus as a listener. The
controller sends UNL automatically after the device has
successfully received a device-dependent or common command.
"Unaddresses" a specific device on the bus as a talker. The
controller sends UNT automatically after it receives the response
from a device-dependent or common query.
Remote Commands
Function
6
Using Commands
6-9