20
Some screen items are marked with a double
−
headed arrow (a split diamond) when selected to
indicate that the item’s setting can be changed by further presses of the soft
−
key, by pressing
either cursor key or by using the rotary control. For example, pressing FILTER brings up the
screen shown below.
FILTER SETUP
mode: auto
◊
type: 10MHz eliptic
Repeated presses of the
mode
soft
−
key will toggle the mode between its two possible settings
of
auto
and
manual
. Similarly, when
type
is selected, repeated presses of the
type
soft
−
key (or cursor keys or use of the rotary control) will step the selection through all possible
settings of the filter type.
In addition to their use in editing items identified by a double
−
headed arrow as described above,
the CURSOR keys and ROTARY CONTROL operate in two other modes.
In screens with lists of items that can be selected (i.e. items marked with a diamond) the cursor
keys and rotary control are used to scroll all items through the display if the list has more than
three items; look, for example at the STD (standard waveform) and UTILITY screens.
In screens where a parameter with a numeric value is displayed the cursor keys move the edit
cursor (a flashing underline) through the numeric field and the rotary control will increment or
decrement the value; the step size is determined by the position of the edit cursor within the
numeric field.
Thus for
STANDARD FREQUENCY
set to
1.00000 MHz
rotating the control will change the
frequency in 1kHz steps. The display will auto
−
range up or down as the frequency is changed,
provided that autoranging permits the increment size to be maintained
;
this will in turn determine
the lowest or highest setting that can be achieved by turning the control. In the example above,
the lowest frequency that can be set by rotating the control is 1 kHz, shown on the display as
1.000000 kHz
.
This is the limit because to show a lower frequency the display would need to autorange below
1kHz to
xxx.xxx Hz
in which the most significant digit represents 100Hz, i.e. the 1kHz
increment would be lost. If, however, the starting frequency had been set to
1.000000 MHz
,
i.e. a 100 Hz increment, the display would have autoranged at 1kHz to
900.0000 Hz
and
could then be decremented further right down to
000.0000 Hz
without losing the 100 Hz
increment.
Turning the control quickly will step numeric values in multiple increments.
Principles of Operation
The instrument operates in one of two different modes depending on the waveform selected.
DDS mode is used for sine, cosine, haversine, triangle, sinx/x and ramp waveforms. Clock
Synthesis mode is used for square, pulse, pulse train, arbitrary and sequence.
In both modes the waveform data is stored in RAM. As the RAM address is incremented the
values are output sequentially to a Digital
−
to
−
Analogue Converter (DAC) which reconstructs the
waveform as a series of voltages steps which are subsequently filtered before being passed to
the main output connector.
The main difference between DDS and Clock Synthesis modes is the way in which the addresses
are generated for the RAM and the length of the waveform data.
