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SECTION
2.
INTERNAL DATA STORAGE
The Data
Storage Pointer
(DSP) is used to
determine where to store
each new data point
in
the Final Storage
area. The
DSP advances to
the next available memory location alter each
new
data point
is
stored.
The DPTR is used to recall data to the
LCD
display. The
positioning
of
this pointer and data
recallare controlled from the keyboard (*7
Mode).
The
TPTR is used to control data transmission
to a cassette
tape recorder. When on-line tape
transfer is activated
(.4
Mode
or Instruction
96,
option
O0),
data
is
transmitted to tape
whenever
the DSP
is
a minimum
of 512 memory locations
ahead of the
TPTR.
The
TPTR may also be
positioned via
the keyboard for manually
initiated data transfer to
tape (.8 Mode).
The PPTR is used to control data transmission
to a printer, Storage Module, or other serial
device.
Whenever on-line printer
transfer
is
activated
(.4 Mode or Instruction 96), data
between
the PPTR and DSP are transmitted.
When on-line transfer
to a SM192/716 Storage
Module
is
activated
by Instruction 96 with output
code 30,
data
is
transmitted each time an output
array is stored
in FinalStorage lF THE
STORAGE
MODULE
IS
CONNECTED TO THE
21X. ll the
Storage Module is
not
connected,
the 21X
does
not
transmit
the data nor does
it
advance
the PPTR to the new DSP
location.
lt
saves the
data
untilthe
Storage Module
is
connected. Then, during the next execution of
Instruction 96, the 21X outputs all
of
the data
between
the PPTR and the DSP and updates
the PPTR to the DSP location (Section 4.1)
The MPTR is used
in
transmitting data over
a
telecommunications interface. When
Telecommunications
is
first entered, the MPTR
is
set to the
same location as the
DSP.
Positioning
of
the MPTR
is
then controlled by
commands from
the external calling device
(Section 5.1).
2-2
NOTE: All
memory pointers are set to the
DSP location when the
datalogger
a
program.
For
this reason, ALWAYS
RETRIEVE UNCOLLECTED DATA
BEFORE MAKING PROGRAM CHANGES.
For example, assume the
TPTR lags the
DSP by less than 512 data points when the
datalogger program is
altered.
On
compiling, the
TPTR is positioned with the
DSP, losing reference to the data that was
intended
to
be
transferred
to
tape.
The
data is not automatically transferred and
appears as a discontinuity
in
the data file.
Untilthe
ring memory wraps around and
data overwrite occurs, the data may
be
recovered using
the.8
Mode.
This
scenario
is
also true for
the PPTR and data
intended for
a Storage Module.
2.2
DATA OUTPUT FORMAT AND
RANGE LIMITS
Data are stored internally in Campbell
Scientific's Final Storage Format (Appendix
C.2).
Data may be sent
to Final Storage
in
either LOW RESOLUTION or HIGH
RESOLUTION
format.
Low resolution
is
the
default.
To change
the resolution, Instruction
(Section
1
1) must precede
the Output
Instructions in
the program table.
2.2.1
RESOLUTION
AND RANGE LIMITS
Low resolution data is
a
2 byte format with
3
or
significant digits and
a maximum magnitude of
t6999.
High resolution
data
is a
4 byte format
with
5
significant digits and
a maximum
output value
of
t99999
(see
Table 2.2-1 below).
TABLE
2.2-1. Resolution
Range
Limits of
21X Data
Minimum
Resolution
Zero
Magnitude
Low
0.000
+0.001
0.0000
+.00001
Maximum
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