Bus Description - HP 5340A Operating And Service Manual

followed by the appropriate multiplier to make the reading Hz, and a word terminator. Table 2-5
lists the order outputed and a description of the 16 output characters.

2-20. Bus Description

2-21. The 15-line bus consists of 8 data lines plus 7 control and status lines. Addresses, program
and output information are communicated on the data lines. These are based on a character-serial,
seven-bit ASCII code set.
2-22. Three control lines are used to execute the transfer of each byte of information on the data
lines. They employ a n interlocked "handshake" technique to
asynchronous data transfer without timing restrictions being placed on either the 5340A or its
controller. One line is driven by the 5340A to inform the controller of
uses the three remaining lines to manage the 5340As on the bus.
2-23. Several 5340A's can be connected to a common bus. The exact number depends on the
drive capability of the controller (see LINE CHARACTERISTICS). A specific 5340A is made to
send output data (TALK)
or
2-24. All bus lines have been given names and mnemonic acronyms that convey the message
being carried on that line. Each line is described below, followed by Table 2-1 which lists the
relationship of the Attention line and the three handshake lines. Figure 2-1 shows the signal
levels and timing relationship of the handshake and data lines. A L L INSTRUMENTS CONNECT-
ED TO THE BUS, INCLUDING THE CONTROLLER, MUST OBEY THESE DESCRIPTIONS.
a. SERVICE REQUEST (SRQ)
By setting SRQ low, a 5340A indicates to the controller that it has completed a measure-
ment and is ready to output. It drives SRQ only if programmed to "WAIT" in the output
phase of its operating cycle until addressed to output. When programmed in the other
output mode "output ONLY I F addressed", the 5340A sets SRQ high at all times. When
SRQ is high, service is not being requested.
If two or more 5340A's are connected to the bus and one of them sets SRQ low, the
controller must go through a process of elimination to determine which one requested
service. It does this by addressing each one to TALK in a n orderly manner. Only the
b. REMOTE ENABLE (REN)
REN can be used by a controller to select remote or local (front panel) control of the
operating of a 5340A. I t works in conjunction with the information stored in the local-
remote program storage cell (see Table 2-4). When REN is low and the 5340A has
been sent a n ASCII "0", it will operate according to the information previously stored
in its remote-local program storage cells. It operates according to its front panel con-
trols for all other combinations of these, i.e., REN is low and the remote-local storage
cell contains a n ASCII "N" or when REN is high regardless of what is stored in the1
remote-local cell. ASCII "N" is stored in the local-remote program storage cell when
either the power is turned on or the RESET pushbutton is depressed.
c. INTERFACE CLEAR (IFC)
A controller uses IFC to clear the bus. When it sets IFC low for >lo0 psec, all 5340A's
immediately stop driving the data lines (DIO1 through DI07) and handshake lines
(RFD, DAC, and OAV). IFC will not clear a 5340A's service request (SRQ). A con-
troller may dride IFC low at any time. When IFC is high, it has no effect on the bus
operation. The 5340A monitors IFC at all times.
accept program data (LISTEN) by addressing it to do so.
Model 5340A
Installation and Remote Programming
information. This allows for
pass
its
status. The controller
2-3