DH Instruments COMPASS FOR MOLBOX, Руководство пользователя

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COMPASS

for molbox™ User’s Manual
Page 145
© 1998-2003 DH Instruments, Inc .
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13.1 OVERVIEW
The ability to communicate quickly and simply with a wide variety of instruments is one of the most
important features of
COMPASS . Without this capability, the benefits of automation could not be fully
realized as data acquisition and control functions would still have to be performed manually.
This section provides information on COMPASS’s facilities for interfacing with remote instruments. This includes
how commands are sent to instruments, the formatting of responses, troubleshooting tips and overall
interface timing.
COMPASS supports remote communications over RS-232 and IEEE-488 interfaces. In general,
initialization, set and read command sets with up to 10 discrete commands per set can be issued to
complete a desired function. In many cases, multi-command sets are not needed.
COMPASS’s highly
versatile command structuring support and the near universality of RS-232 and/or IEEE-488 interfaces on
today’s computers and test instruments, make it possible to use just about any test instrument with
remote communications capability with
COMPASS .
There are two main interface types set up in COMPASS . Read interfaces are used when COMPASS
must acquire data from a device such as a digital multimeter used to read a DUT’s output. Set interfaces
are used to send flow setting commands directly to a flow controlling device or a programmable power
supply. Each of these main interface types usually include two command sets: a) the
initialization to
prepare to the device to set or read properly (not needed in all cases but indispensable in some); and b)
the
actual read or set instructions. Read interfaces must always be set up so that the device responds
in a specific, preplanned measurement unit; set interfaces must be structured to include a variable which
is the numerical value of the set target since the target value changes at different points in a test.
Most devices that support remote interfacing use a common text command and response format.
Typically, commands are word fragments that resemble the function of the command. Responses to
numerical query commands frequently output as a direct numerical value or a condensed string with the
number embedded. Some instruments require ASCII control codes as part of the command set. Control
codes are specified in the instrument documentation as non-printable hexidecimal characters, e.g., 04H
or H04.
COMPASS is designed to handle all of these cases. The <Leading characters to strip> , <Set
Unit Variable> and <Insert Special Character> features can be used to support any interfacing protocol.
However, <Read Command> responses from instruments that do not directly include the numerical value
of the devices’ output in the output units are not supported. This applies only to commands which require
an output. The output of all other commands is ignored.
It is critical to check the <No Response> option for commands that do not respond. This will prevent
COMPASS from timing out while waiting for a response.
All remote commands must be entered contiguously. The first blank command entry is assumed to be
the end of the command list even if commands are specified beyond the blank entry.
Up to 10 commands can be issued as part of the initialize, read or set command setup.