Campbell Scientific TX312 High Data Rate GOES Transmitter - Manual (Page 31)

TX312 Transmitter
of repetitions has been met. When properly configured, the TX312 will ensure
the data is transmitted on the correct channel, at the correct baud rate and at the
correct time without overrunning the transmit window.
The datalogger will interface with the TX312 under program control. Two
program instructions are used, P126 and P127. P126 is used to send data to a
buffer. New data is either added to existing data (append) or overwrites
existing data. In overwrite mode, all data in the buffer is erased before new
data is written. P127 is used to retrieve information from the TX312.
Information regarding GPS time, latitude and longitude can be retrieved and
stored in the datalogger. Information regarding the status and past errors can
also be retrieved.
Data that is sent to the self-timed buffer 60 seconds or more before transmit
time will be transmitted on the next scheduled transmission; otherwise, the data
will be scheduled for a later transmission.
5.2.1 Deciding How Much Data will be Transmitted and When
The amount of data that can be transmitted depends on several factors: the
transmit window length, the transmit baud rate, and the data format. The
transmit window limits the time available for data to be sent. The baud rate
determines how fast data is sent. The data format determines how many bytes
are required per data point.
The maximum number of data points that can be sent is estimated with this
formula:
b(a-2)/8c = total number of data points per transmission
Where:
a = window length in seconds
b = baud rate or bits/second; i.e., 100, 300, or 1200
c = bytes per data point
Binary data uses 3 bytes per data point.
ASCII data uses 7 bytes per data point.
The Sat Commander Software includes a Command to read the Max Timed
Message Length, which will use the TX312 to calculate the maximum number
of bytes to be sent, not the maximum number of data points. To use the
software to calculate the maximum number of data points that can be sent, first
setup the transmitter, then use the max timed message length command. Take
the result and divide by 3 if the data format is pseudo binary or divide by 7 if
using an ASCII format.
5.2.2 Deciding What Data Format to Use
The choice of data format effects two areas. First, the data format effects how
much data can be sent in a single transmission. Binary data formats require 3
bytes per data point. ASCII data formats require 7 bytes per data point.
Second, binary data must be decoded after transmission, ASCII does not. The
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