Fluke 5700A Series II - Interface Messages

5700A/5720A Series II
Operators Manual
5-58
5-43. Interface Messages
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 5-9 lists the interface messages that
the calibrator accepts. Table 5-9 also shows the BASIC statement you execute on some
controllers to generate the interface message. Table 5-10 lists the interface messages that
the calibrator sends. The mnemonics listed in the tables are not sent in BASIC PRINT
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's interface itself as each byte is sent over the bus.
Table 5-9. Interface Messages Accepted by the Calibrator
Mnemonic Name Function Related Controller
Command
ATN Attention 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.
None
DAC Data Accepted Sets the handshake signal line NDAC low. None
DAV Data Valid Asserts the handshake signal line DAV. None
DCL Device Clear Clears the input/output buffers. CLEAR
END End A message that appears when the controller
asserts the EOI signal line before sending a byte.
None
GTL Go To Local Transfers control of the calibrator from one of the
remote states to one of the local states (See
Table 5-5.)
LOCAL
LLO Local Lockout Transfers remote/local control of the calibrator.
(See Table 5-5.)
LOCKOUT
IFC Interface Clear A control line that sets the interface to a
quiescent state.
INIT
MLA My Listen Address Addresses a specific device on the bus as a
listener. The controller sends MLA automatically
whenever it directs a device-dependent of
common query to a specific instrument.
None