The total programming time depends
on the selection
of the interface modes. In some
modes,
programming steps are
performed in parallel
and can increase throughput. The
following
paragraphs give
some
typical
timing data for
the above four programming
steps and describes
how the interface
modes affect their relative
timing.
2-66.
TRANSFER OF
COMMANDS
TO
GENERATOR
The maximum rate of transfer
is 0.4 to 0.5 ms
per character. With most IEEE-488
controllers,
all characters
sent with a single output
or print statement is
transferred together at the
maximum rate. The total time
to transfer commands
to the Generator is obtained
by
multiplying the number
of characters by the rate
of transfer.
2-67.
COMMAND-PARSING TIME
Command-parsing time is the
sum of the time required
to process the header, the numeric,
and
the suffix. Some
commands do not have numerics
or suffixes. Table
2-
1
9
gives the
typical time
it takes
to process the different
components of a command.
2-68.
SOFTWARE
PROGRAMMING TIME
The minimum
time required to process
a command is 25 ms. Most of the commands
that do
not program
the hardware (such
as storing step values) are programmed
in 25 ms. Table
2-20
gives the typical time value
for programming the different
functions in the Generator.
2-69.
INSTRUMENT-SETTLING TIME
The software-programming time
typically exceeds the
setting time of the RF circuitry,
therefore the instrument-settling
time can generally
be excluded from throughput calculations.
The exception
is when level correction is
disabled. Disabling level
correction reduces the
software-programming time
by 10 ms but does not affect the
switching time of the frequency
programming circuitry.
A 10 ms settling delay should
be added if level correction
is
disabled
and a settled
RF output is required.
2-70.
TIMING OPTIMIZATION
Timing depends
upon the interface modes selected.
Refer to the paragraphs on Interface
Mode
Commands
for a complete description
of the interface modes.
The transfer
of commands from the IEEE-488
controller to the Generator
can never be
processed
in
parallel
with
anything else.
The transfer of commands usually
happens
simultaneously, regardless
of which interface mode is selected.
The parsing of the command
and programming the new instrument
state is performed one
message unit
at a
time.
The record mode selects
a
command
or a record as the message unit.
The record
mode off (“RMO”) is slower since
there is extra processing between message
units,
and the message unit is smaller.
If the valid
mode is enabled, the processing
of message units is delayed until the Generator
has
settled
from the previous message.
While the RF output is typically settled before the software
finishes processing the
command, enabling the valid mode
adds an additional delay to ensure
that the
output is settled before the next command
is processed.
If the output of the Generator
does not need to be settled between programming
strings, the
valid mode should
be turned off to speed up processing.
If the output does not need to be
settled between
commands, but needs to be
settled between records, enable the valid mode and
the record
mode. The instrument processes
commands within the record as fast as possible and
waits for the output to settle
only between records.
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