Chapter 6, COMPUTER OPERATION
6-29
been sent, equivalent to asserting bits 0 and 2, then the X and Magnitude outputs
would be stored. The permitted values of n would therefore be 0 and 2, so that DC 0
would transfer the X channel output curve and DC 2 the Magnitude curve.
NOTE: When transferring the Frequency curve, which is saved when bit 15 in the
CBD parameter is asserted, the instrument automatically reads the data for each
stored point in both frequency curves (i.e. the lower and upper 16 bits) and sends it
as a single data point.
Fast Mode
Only fixed point mode is supported. One curve at a time is transferred, with the
selected curve being dumped via the computer interface in decimal format.
The value of n defines the curve to be transferred according to the following table:
n Output and range
0 X Output (±10000 FS)
1 Y Output (±10000 FS)
2 Main signal channel ADC output (digital signal monitor 1
3 ADC1 (±10000 = ±10.0 V)
4 ADC2 (±10000 = ±10.0 V)
Dual modes only:-
5 X
2
Output (±10000 FS)
6 Y
2
Output (±10000 FS)
7 Input to second demodulator (digital signal monitor 2)
The computer program's subroutine which reads the responses to the DC command
needs to run a program loop that continues until all the data has been transferred.
DCB n Dump acquired curve(s) to computer in binary format
The operation of this command depends on whether data has been stored into the
Standard or Fast Mode curve buffers.
Standard Mode
This command causes a stored curve to be dumped via the computer interface in
binary format, using two bytes per point. All curves other than the lower 16-bits of
the reference frequency curve (curve 15) use 16-bit 2’s complement encoding, and
all data points are sent with the MSB first. The number of data bytes sent is therefore
equal to twice the current curve length. Each point is sent in fixed point mode, there
being no floating point version of the command, and hence if floating point values
are required the user may need to additionally store and read the Sensitivity curve
and then perform the correction in his own software. In order to achieve the
maximum transfer rate, no terminators are used within the transmission, although the
response is terminated normally at the end.
One curve at a time is transferred. The value of n is the bit number of the required
curve, which must have been stored by the most recent CBD command. Hence n can
range from 0 to 16 in Single Reference Mode, and 0 to 21 in the dual modes. If for
example CBD 5 had been sent, equivalent to asserting bits 0 and 2, then the X and
Magnitude outputs would be stored. The permitted values of n would therefore be 0
and 2, so that DCB 0 would transfer the X channel output curve and DCB 2 the
Magnitude curve.
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