Campbell Scientific ST-21 Argos Satellite Transmitter - Manual (Page 8)

ST-21 Argos Satellite Transmitter
TABLE 1-1. ST-21 Serial Port Configuration
Pin number Function
1 +5 volts
2 Ground
3 NC
4 TXD
(data out)
5 NC
6 SDE
(input)
7 CLK/HS (input)
8 +12 volts
9 RXD (data in)
FIGURE 1-2. The ST-21’s 9-pin connector attaches to the datalogger
via the SC12 cable
1.3 Data Buffers
The ST-21 has 8 internal data buffers. Before a data buffer can be used, a valid
Argos ID number, repetition rate and frequency must be assigned to the buffer.
The Argos ID numbers must be entered as a decimal and a Hexadecimal
number. The ST-21 uses the Hexadecimal format to determine if the ID is a 28
bit ID number. When using 28 bit ID numbers, 31 bytes of data can be stored
in the buffer. When using 20 bit ID numbers, 32 bytes of data can be stored in
the buffer. The data buffers are numbered 0 through 7, with 7 being reserved
for other uses.
Data buffer setup can be done by the factory or under datalogger control. The
factory settings are stored in non-volatile memory. Settings that have been
changed by the datalogger are erased when the ST-21 resets.
1.4 Multiple Argos ID Numbers
The use of multiple ID numbers can significantly change how the datalogger is
programmed. When multiple ID numbers are used, the ArgosTransmit()
function works best. When ArgosTransmit() is executed, the contents of the
specified data buffer are transmitted once. ArgosTransmit() gives full control
of timing of transmissions to the datalogger programmer. Special care must be
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