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Example, calculating the CRC in the DMPAFT example above:
Old CRC Data byte Table index
Table Value New CRC
0x0000
0xC6
(0x00 ^ 0xC6) = 0xC6
0xB98A
(0x0000 ^ 0xB98A) = 0xB98A
0xB98A
0xCE
(0xB9 ^ 0xCE) = 0x77 0x0E70
(0x8A00 ^ 0x0E70) = 0x8470
0x8470
0xA2
(0x84 ^ 0xA2) = 0x26
0x44A4
(0x7000 ^ 0x44A4) = 0x34A4
0x34A4
0x03
(0x34 ^ 0x03) = 0x37
0x46B4
(0xA400 ^ 0x46B4) =
0xE2B4
If you continue processing the received CRC value of 0xE2B4 it will look like this:
Old CRC Data byte Table index
Table Value New CRC
0xE2B4
0xE2
(0xE2^ 0xE2) = 0x00
0x0000
(0xB400 ^ 0x0000) = 0xB400
0xB400
0xB4
(0xB4^ 0xB4) = 0x00
0x0000
(0x0000^ 0x0000) =
0x0000
The final CRC of zero indicates that the "packet" passed its CRC check.
XII.
EEPROM configuration settings
There are two different ways to access data from the EEPROM. The commands "
EERD
" and
"
EEWR
" provide a text based interface that you can use with a terminal emulation program, such
as HyperTerminal. All numerical data is sent and received as ASCII strings that represent
hexadecimal numbers. You can read as many values as you want with one "
EERD
" command, but
you can only write one byte of data for each "
EEWR
" command.
The commands "
EEBRD
" and "
EEBWR
" use similar hex strings to specify what data you want to
read or write, but the actual EEPROM data is send and received as binary bytes. You can read
and write as many bytes as you would like to in a single command.
Both read and written data includes a CRC code. A CRC is required for data written with the
"
EEBWR
" command.
There are several EEPROM data locations that should not be written with the "
EEWR
" or "
EEBWR
"
commands. These are either factory calibration values that should not be changed, or else they
are values that can be set from a different command. For example, use the "
SETPER
" command to
set the ARCHIVE_PERIOD value, and the "
BAR=
" command to set the BAR_CAL and
ELEVATION values. It is safe to read these EEPROM values.
The table below gives the addresses and sizes of the most useful EEPROM data values. The
address of each field is given both in decimal and in hex. Use the hex value in all "
EE...
"
commands. There is a supplemental list of the locations where the Vantage graph data is stored
in section XIV.
