Geometrics G-822A, Руководство по эксплуатации

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Geometrics, Inc. G-822/G-823 Magnetometer Manual
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Three pieces of information are needed to select and turn on/off an A/D channel: The
counter #, the channel number, and a flag indicating whether to enable or disable that
channel. The enable/disable flag is sent first (after the 'A' command identifier). A '0'
character will turn off the channel, a '1' turns it on. The next character specifies the channel
number (0-7), followed by 2 characters indicating the counter number (00-19). If the
counter number is not sent then it defaults to counter 0.
Baud Rate Change
The baud rate can be commanded to change by giving a 'B' command character followed by
5 more number characters specifying the desired baud rate. Valid baud rate commands are:
'B19200', 'B09600', 'B04800', 'B02400', 'B01200', 'B00600', and 'B00300'. This command
will not execute until the entire command has finished echoing out to the next
counter/logging device. This allows the command to propagate through all counters and be
implemented before output data arrives at a different rate.
Output Format Select
The default (ASCII) output format is described in detail at the beginning of this
document. This is the easiest format to view and import into various processing utilities.
It is also very inefficient in terms of disk storage space and time required to transmit each
cycle. There are three other output formats that can be used as well:
Packed BCD
Packed BCD format throws away all commas, decimals, spaces, and the magnetometer
most significant byte ('1' if more than 100,000 nT, or a blank is less than 100,000nT). The
Preamble character is left alone. In addition all numeral characters (ASCII codes 30 hex
through 39 hex) have the upper nibble (always a 3) discarded and two lower nibbles
combined to form one byte. Finally, the carriage return, line feed sequence is replaced with
a single terminating character '*' (2A hex).
It is very difficult to show what these files would look like if displayed on a computer
screen since each type of computer would display these binary characters differently. Many
of these binary characters would be interpreted as screen commands which might ring the
bell or clear the screen. Therefore it is necessary to convert ASCII printouts to hexadecimal
numbers to show the Packed BCD format.
An ASCII counter output of:
'$ 54369.127,1234,5678,0000' (plus carriage return line feed)
converted to hexadecimal numbers would be:
24 20 35 34 33 36 39 2E 31 32 37 2C 31 32 33 34