HP 5501A Operating And Service Manual page 107

lnstructions are sent from card to card over an eight-bit-wide instruction bus and two status
lines called Instruction Valid (INSV) and Operation Complete (OPC). lnstructions consist of
two parts: a four-bit alpha address and a four-bit numeric command. Each card in the system
has its own address, fixed in some cases and selectable by means of jumpers or switches in
others. The modules and their addresses are:
Module Address
10745A HP-IB Interface
.................................
., .,
................
0
10746A Binary I/O
.........................................................
P
10755A Compensation Interface
............................................
V
10760A General-Purpose Counter
..............................
X,Y,Z,A,B, or C
10763A Multiplier
..........................................................
M
10762A Comparat~r
...........................................
X,Y,Z,A,B, or C
10763A English/Metric Pulse Output
...........................
X,Y,Z,A,B, or C
...................................
10764B Fast Pulse Converter X,Y,Z,A,B, or C
In general, a particular numeric command always has the same meaning. However, different
modules respond differently to the same command. An important concept here is that of im-
plied talkers and listeners.
One way to handle communications in a bus-oriented system i s to address one module a s talker
and one or more modules a s listeners. This requires two modes of operation, one for addressing
and one for data transfer.
For example, we can make the instruction lines separate from the data lines and agree that
all modules will continuously monitor the instruction lines, looking for and reacting to only
those instructions that concern them and ignoring those that do not. This means that
a
partic-
ular instruction will have any of several meanings, depending upon a particular card's point
of view.
As an example, consider the instruction "2X". The address portion is "X", which could desig-
nate an X-axis counter card in the system. From the point of view of the X-axis counter the in-
struction "2X" means that it should enable its data output buffers, its decimal point position
code drivers, and its error flag drivers to the 10740A backplane and set the Binary Data Valid
line true. To a 10745A HP-IB lnterface card it means load this information into your data re-
gister, decimal point code register, and error flag register, and issue a service request (SRQ)
if there has been an error. To a 10761A Multiplier, however, it says take the data being output,
multiply it by the laser light wavelength corrected for changes in the index of refraction of
air, and store the result. The X-axis counter card was the implied talker and the multiplier
and I/O card were the implied listeners. I t was not necessary to address the counter a s a
talker or the 1 / 0 and multiplier as listeners.
There are four lines on the 10740A backplane that are dedicated to particular functions and
always have the same meaning. Two are nonaddressed commands and two are status lines.
System Reset is the command to initialize to some starting condition. This command is gener-
ated by the interface modules during power-up; it can also be sent by the system controller.
Synchronous Sample i s the command to take present displacement information and load it
into output buffers. It is used to get a simultaneous sample from all axes. A-Mode is a status
code from counters and comparators, indicating to the multiplier card whether quarter-wave
(A/4) or eighth-wave (A/8) resolution is being used in the system. System Null is a status
code from comparators, indicating the system has arrived at the required destination. For
additional information and schematics, refer to the 10740A Coupler Operating and Service
Manual.