Table of Contents
Advertisement
Chapter 6, COMPUTER OPERATION
DCCOUPLE [n]
DCB n
6-30
Input coupling control
The value of n sets the input coupling mode according to the following table:
n
Coupling mode
0
AC coupled
1
DC coupled
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.
Curves 15 and 16 store the reference frequency in millihertz. When using the DCB
command (although not with the other curve transfer commands), both curves need
to be transferred separately. They should then be converted to two arrays of integer
values, allowing for the fact that the data points in curve 15 are unsigned 16-bit
values, while those in curve 16 are signed 2's complement 16-bit values (although in
practice they are never negative). Finally they should be assembled into a single
curve using the following algorithm:
Reference Frequency = (65536 × value in Curve 16) + (value in Curve 15)
The computer program's subroutine which reads the responses to the DCB command
needs to be able to handle the potentially very large data blocks (200 k bytes in the
case of one 100 k curve) that can be generated.
NOTE: When using RS232 communications, the interface must be set to use 8
data bit transmission.
Fast Mode
One curve at a time is transferred, with the selected curve being dumped via the
computer interface in binary format, using two bytes per point. Data is sent using 16-
bit 2's complement encoding, with the MSB sent first.
The value of n defines the curve to be transferred according to the following table:
Advertisement
Table of Contents
