Data Transfer Example; Basic Talker Functions; Basic Listener Functions; Figure 4-2 Handshake Timing Diagram - Keithley 3321 Operator's Manual

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SECTION 4
GETI Interface
NRFD
(Listener)
DAV
(Talker)
Ready for next Data in
Data Processing
Data Bus Disabled
Data Bus Enabled
(Listener)
NDAC
Data Bus
Signal
T I",
Termination of
I
$3
Data Reception
Data not received
(In Data Reception)
0 '
t
Valid Data
0 Indicates that all listeners are waiting for data.
@ The talker outputs data to be sent to the data lines.
@ The talker checks NRFD and if high, DAV is set low to indicate to the listener that data is valid.
@ When the DAV goes low, the listener reads data and NRFD is set low,
indicating to the talker that data processing is in progress. Each listener sets
NDAC high at the completion of data input. The NDAC of the bus is the OR
function of the NDACs from each listener.
@ When all listeners have completed receiving data, NDAC goes high (result of
the OR output) indicating to the talker that data reception has been completed.
@ The talker sets DAV high indicating to the listener that the data on bus is not valid.
@ The listener checks whether DAV is high and sets NDAC low, completing the handshake.
@I Indicates that all listeners have completed data processing and is waiting for next data.
Figure 4-2. Handshake Timing Diagram
4.1.4 Data Transfer Example
Whenever the talker address of another device is re-
ceived.
Figure 4-3 provides a data transfer example using the
three-line handshake process. In this example, the data
"ABC" is sent, followed by the delimiter "CR/LF".
Whenever the device is specified as a listener.
Whenever untalk (UNT) is received.
Whenever IFC is received.
4.1.6 Basic Listener Functions
4.1.5 Basic Talker Functions
l
Only one talker may exist on the GPIB at any time.
l
When the controller ATN signal is high, data is sent to
the listeners.
l
Source handshaking is performed automatically.
l
A service request (SRQ) is sent to the controller.
l
The talker function is enabled for both the local and re-
mote modes.
l
The talker function is canceled by any of the following:
l
Two or more listeners may exist on the GPIB at any
time.
l
When the controller ATN signal is high, data is re-
ceived from a talker.
l
Acceptor handshake is performed.
l
The listener function is canceled by any of the follow-
ing:
Whenever the device is specified as a talker.
Whenever unlisten (UNL) is received.
Whenever IFC is received.
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