The 1251 Multichannel Analyzer System 1250 Frequency Response Analyzer
16-8 AMK/1250/1
16.7.3 SETTING UP THE GPIB CONFIGURE MENU
The GPIB is set up for remote operation from the GPIB CONFIGURE menu of the host
1250, accessed via the DATA OUTPUT key. Use of this key is fully explained in
Chapter 12, Section 1. Configuring the 1250 for Service Request generation. Serial
and Parallel Poll is covered in Chapter 13, Sections 12 and 13; the 1251 Units do not
affect this setting up process.
The selection of Output Separator and Terminator characters made on the 1250 reflects
through all 1251 Units. The data output type on the 1251 is selected as follows:
1250 SELECTION 1251 OUTPUT
off off
all all
pass all
fail all
dump dump
i.e. limit checks cannot be carried out on the 1251. To apply a limit check to data from a
1251 channel, the data must be output via the 1250.
Important: When the required GPIB configuration has been set up on the 1250, press
the BREAK key on the front panel, or send the BREAK command via the GPIB
Interface. Allow one second's delay before the next action, because BREAK resets the
GPIB hardware in the 1250 and 1251 Units. This transfers the GPIB configuration
settings to all 1251 Units, via the 1250-1251 Interface Bus.
16.7.4 DATA TRANSFER SPEEDS
The maximum data transfer rate across the GPIB port of the 1250 is approximately
1000 characters (bytes) per second, whereas a 1251 Unit achieves a rate of
approximately 100,000 characters per second.
For the sake of speed, readings are always automatically output in blocks of eight
channels even if not all eight channels are fitted. Missing channels output results of
'zero'. The software in the external Controller must select the required data from the
standard fixed-format blocks presented to it by the 1251 Unit.
16.7.5 GPIB OUTPUT BUFFERS
The operation of reading data from the GPIB output buffer is also different in the 1251
compared to the 1250 Unit.
In the 1250, once data has been read from the GPIB output buffer, it is not possible to
access the buffer again until new data is available. This allows the Controller to wait for
new data by holding on a READ statement.
In the 1251 Unit, however, data in the GPIB output buffer can be accessed repeatedly,
which could cause old data to be read into the Controller. To ensure that this does not
happen, the 1250 may be configured to generate a Service Request when new data is
available. The Controller then waits for Service Request before reading data from the
1251 Units. The 1251 data changes only when a new measurement is taken (i.e. via
Single) or when the "order" is changed.
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