HP 3336A Operating Manual page 40

6
Model 3336A/B/C
3-116. Handshake Lines (DAV, NFRD, NDAC). Data is transferred between devices using
an interlocked HANDSHAKE technique. This method causes the data to be moved at a rate
determined by the slowest device involved in the transfer. The HANDSHAKE lines coor-
dinate the asynchronous data transfer by communicating the status of the transfer to the
device sending the data (talker), the device receiving the data (listener) and the device con-
trolling the transfer (controller).
3-117. General Interface Management Lines. These five lines operate independently and in
conjunction to send Bus Management Message to the devices connected to the HP-IB. Each
line has a precise definition that is either sent or not sent depending on the truth state of the
line. The lines are defined as follows:
Attention (ATN)—When TRUE, identifies ASCII characters on the DATA lines as
commands. Identifies ASCII characters on the DATA lines as data when FALSE.
Remote Enable (REN)—Places the interface bus in the REMOTE mode.
Interface Clear (IFC)—Halts all activity on the HP-IB.
Service Request (SRQ)—A device on the bus uses this line to request service from the
controller.
End or Identify (EOI)—Indicates the last character of a multi-byte message.
Also used with ATN (true) to indicate a parallel poll.
3-118. Producing Controller Statements for Instrument Operation.
3-119. The interface between the operator and the instrument is changed dramatically when
an instrument is operated over the HP-IB. During non HP-IB operation, the operator ac-
tuates front panel controls that are labeled according to function. Often, only a single con-
trol is used to activate a function and getting the results of a measurement simply consists of
reading the display! In contrast, during HP-IB operation, the operator typically faces an
alpha-numeric keyboard. Neither the key functions nor their labels correspond to the instru-
ment operation. The natural question arises:
''What instructions must be entered on the controller to cause a
particular action in the instrument?"'
This sub-section explains how to answer that question.
3-120. An ideal HP-IB operating section in an instrument manual would include specific in-
structions such as:
'*To set the frequency of the -hp- 3336 to 19.5 MHz, enter wrt 704,
'"*FR19.5MH"' on the controller.''
This instruction is very specific and leaves no room for error. Unfortunately, it is not possi-
ble to supply such specific instructions because it is not possible to predict which instruments
and controllers will be used together. The instrument's operating instructions, therefore, can
only describe how the instrument interfaces with the HP-IB. An analogous situation exists
for the controller's operating instructions. Almost all statements sent over the HP-IB to
operate an instrument, contain a portion that depends upon the individual instrument, and a
portion that depends upon the controller used in the system. The operator must produce the
required statement from information found partially in the controller documentation. The
concept of Bus Messages, presented in the next paragraph, is a significant aid to this process.
Operation