Table of Contents
Advertisement
21-15.
Command Structure.
Each command consists of a two letter definition prefix followed by a numeric
data field. The data field will vary in length and structure according to the definition prefix as shown in table
21-3. Spaces may be inserted anywhere in the command but are not required. Each letter or number of a
command is transferred from the bus controller to the analyzer in ASCII format. ASCII defines a 7-bit digital
code for each letter, number, and symbol commonly used in computer programming.
21-16.
The first letter of the two letter prefix identifies a command category with the second letter identifying
a particular command within that category. A listing of the command categories and the corresponding first
letter is provided in table 21-2. A complete list of commands is shown in table 21-3.
Table 21-2.
Command Categories
A
c
F
G
K
M
0
R
v
w
Audio Synthesizer
Control
Frequency Counter
Generate/Monitor Control
Keyboard
Modulation
Oscilliscope
Receiver
Voltmeter
Wattmeter
21-17.
The data field is comprised of five sub-fields as shown:
±
n.n
E
±
n
I
DATA SIGN
I
EXPONENT
\
I
""'
EXPONENT MAGNITUDE
DATA VALUE
EXPONENT SIGN
Data limits and accompanying units are given in table 21-3. The data field is optional or not allowed for certain
commands.
21-18.
Data Sign.
The data sign is a single'+' or·-· character indicating the sign of the data value. The sign
may be omitted for positive value data.
21-19.
Data Value.
The data value field is restricted to the numbers '0' through '9' and'.'. A maximum offive
digits to the right and to the left of the decimal point are allowed. The decimal point can be omitted for integer
values. If the value field is omitted, it is assumed to be zero.
21-20.
Exponent.
The presence of the "E" character in the exponent field indicates that the data value is to
be multiplied by 10 raised to the power following the "E" character. If the "E" is omitted the exponent is
assumed to be 10° or 1.
21-21.
Exponent Sign.
The exponent sign is a single +or- character and can be omitted for positive
exponent values.
21-22.
Exponent Magnitude.
The exponent magnitude is a single character 0 through 9. If the exponent
magnitude is omitted, it is assumed to be zero.
21-4
r
l
I
SECTION 21
IEEE - 488 BUS CONTROL
21-1.
INTRODUCTION
21-2. The IEEE Interface Option enables the use of the Communications System Analyzer as a
programmable measurement instrument. When combined with a suitable programmable controller and
applications software, the major functions of the analyzer can be controlled or monitored via an IEEE-488
standard digital interface. Thus, repetitive test routines can be performed and the data recorded quickly and
accurately with little operator interaction.
21-3. The interface characteristics conform to the specifications of the IEEE Standard Digital Interface for
Programmable Instrumentation (IEEE Standard 488) which defines both the electrical and the mechanical
interface. Control protocol is also defined by the specification. Control commands which are unique to the
analyzer are described in detail in the following paragraphs of this section.
21-4. The controller for this application should be capable of reading and writing ASCII and control
characters from and to the bus in accordance with the 488 specification. Application software is the user's
responsibility as dictated by the controller selected, although interface and application assistance is available
from Motorola.
21-5.
The IEEE option package consists of an IEEE Interface module (AS) with a rear panel connector, an
electrically programmable AF attenuator in place of the step attenuator on the AF Input Module (A11), a
fourteen position rotary switch on the front panel in place of the step attenuator shaft, and one additional ROM
memory IC on the Processor module (A9).
21-6. While in the local mode the IEEE-488 equiped system operates and performs the same as a standard
system, except the maximum AF output level is reduced to +11 dBm from +13 dBm. However, when the Remote
Enable (AEN) line on the IEEE Bus is activated many of the front panel controls are disabled and their functions
placed under bus control. Refer to table 21-1 for a listing of those functions which can be controlled or
monitored via the 488 Bus.
21-1
Advertisement
Table of Contents
