HP 8340B Operating Instructions Manual page 88

T8 Acceptors, upon sensing DAV high, set NDAC low in preparation for the next cycle. NDAC goes low as the
first acceptor sets it low.
Tg
First acceptor indicates that it is ready for the next data byte by setting NRFD high (NRFD remains low due
to other acceptors driving it low).
Last acceptor indicates that it is ready for the next data by setting NRFD high; NRFD signal line goes high.
T12 Source, upon sensing NRFD high, sets DAV low to indicate that data on the DIO lines is settled and is valid.
T13 First acceptor sets NRFD low to indicate that it is no longer ready, then accepts the data.
T14 First acceptor sets NDAC high to indicate that it has accepted the data.
T15 Last acceptor sets NDAC high to indicate that it has accepted the data (as at T6).
T16 Source, having sensed that NDAC is high, sets DAV high (as at T7).
T17 Source removes data byte from the DIO signal lines after setting DAV high.
T18 Acceptors, upon sensing DAV high, set NDAC low in preparation for the next cycle. All three handshake
lines return to their initialized states (as at and T2).
Figure 3-26. HP-IB Handshake Timing (2 of 2)
System Control Lines, ATN, IFC, SRQ, REN, EOI
The remaining five lines coordinate communications between the HP-IB LISTENERS, TALKERS, and
CONTROLLERS. The system control lines are used as follows:
ATN, Attention, signals Command Mode when low (True), or Data Mode when high (False). All
devices must monitor ATN at all times and respond to it within 200 nanoseconds. In Command
Mode, the controller is the only talker in the network, while all other devices are listening for
instructions.
When a high (False) ATN signifies Data Mode, data may be transferred along the DIO lines. The
meaning of each data byte is device dependent, and selected by the instrument designer.
IFC, Interface Clear, when low (True) abruptly terminates all HP-IB communications activity: All
talkers and listeners are "unaddressed," and along with the controllers go to an inactive HP-IB
state (the instruments' local functions are not impaired). All devices must monitor IFC at all times
and respond to it within 100 jtsec.
SRQ, Service Request, line is set low (True) by any instrument that needs service from the control¬
ler. An SRQ could result, for example, when an instrument is ready to transmit data upon the
completion of a measurement, or from an error condition. When the controller detects an SRQ it
performs a serial poll of all devices to determine which requested service, and why (polling is
explained in the System Commands). The controller can mask the SRQ to prevent any inconve¬
nient interruptions (as explained in the RE/RM programming codes). The HP 8340B/41B lights a
red SRQ annunciator in the ENTRY DISPLAY when it initiates an SRQ.
REN, Remote Enable, when low (True) enables HP-IB instruments to respond to commands from
the controller or other talkers, when high (False) all devices return to local operation. The HP
8340B/41B lights an amber REMOTE annunciator in the ENTRY DISPLAY when REN is true, and
disables front panel control of the instrument (with three exceptions: the POWER switch can only
be controlled locally, the [LOCAL] key re-enables front panel control unless locked-out by the
controller, and the rotary [KNOB] can be re-enabled by an EK command from the controller). All
devices msut constantly monitor REN and respond to it within 100 ftsec.
HP 8340B/41B
Operating Information
3-85