Operator`s manual

SECTION 2. INTERNAL DATA STORAGE
2-2
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 after each
new data point is stored.
The DPTR is used to recall data to the LCD
display. The positioning of this pointer and data
recall are 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 00), 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 Final Storage IF THE
STORAGE MODULE IS CONNECTED TO THE
21X. If the Storage Module is not connected,
the 21X does not transmit the data nor does it
advance the PPTR to the new DSP location. It
saves the data until the 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).
NOTE: All memory pointers are set to the
DSP location when the datalogger compiles
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.
Until the 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 78
(Section 11) 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 4
significant digits and a maximum magnitude of
±6999. High resolution data is a 4 byte format
with 5 significant digits and a maximum possible
output value of ±99999 (see Table 2.2-1 below).
TABLE 2.2-1. Resolution Range Limits of
21X Data
Minimum Maximum
Resolution Zero Magnitude Magnitude
Low 0.000 ±0.001 ±6999.
High 0.0000 ±.00001 ±99999.