American Magnetics 185 & 186 Liquid Level Instruments (CE-Marked) - Manual (Page 52)

42 Rev. 3
Remote Interface Reference
IEEE-488 Communication Option
5.2 IEEE-488 Communication Option
The IEEE-488 communication option provides a GPIB connector on the
rear panel of the instrument for IEEE-488 (GPIB, HPIB) communications.
5.2.1 Command/return termination characters
All commands are transmitted and received as ASCII values and are case
insensitive. The Model 185/186 always transmits <LF> and EOI as the
termination for return data. The Model 185/186 can accept <CR>, <LF>,
<CR><LF>, <LF><CR>,
or <LF> with EIO as termination characters from
an external IEEE-488 interface.
Only one command at a time should be sent to the Model 185/186 by the
external IEEE-488 interface. Additional commands separated by a
semicolon will not be processed. The instrument uses a single 16 character
buffer for input and output. Consequently, all input strings including
terminations should not be longer than 16 characters. Any excess
characters will be discarded. All alphabetical characters are case
insensitive and character encoding is in accordance with IEEE 488.2.
5.2.2 Communicating with the Model 185/186
The use of a single buffer for both input and output is a result of memory
limitations in the Model 185/186. In order to keep the external IEEE-488
interface from sending successive commands faster than the Model 185/
186 can respond, the Model 185/186 uses the Serial Poll Service Request
(SRQ) to let the external computer know it has finished processing the last
command received and is ready to send a response. This is true of all
commands. Thus sending commands to the Model 185/186 using IEEE-488
protocol is a three step process: 1) send the ASCII command, 2) wait for
SRQ, and 3) get the instrument response.
Note
API’s for some manufacturer’s cards require you to use different
functions to check for SRQ and read the serial poll status (spoll)
byte. Invoking the command to read the spoll byte may be required
to actually clear the SRQ status.
A basic flow diagram for sending an ASCII command to the Model 185/186
and receiving a response is shown on the following page. It is not necessary
to wait exclusively for the SRQ status from the instrument. Other bus
commands can be processed while waiting for the SRQ status from the
instrument.