Xylem XL Series H-522 - Plus - Manual (Page 188)

16-32 Operation with the GOES Radio
XL™ Series
total of 19 bytes per line or 19 bytes per scan. This multiplied by the number of total lines
transmitted (8) give the number of bytes per transmission, 19 * 8 = 152. At 300 baud the 152
bytes would be approximately 6 seconds. This is ok for the 10 second window but would be too
long to fit in a 5 second window. If the data does exceed the window, several things could be
changed; the data could be sent in a binary format, less values could be sent to the Radio, or the
‘Extra Data Sets’ could be set to 0 allowing only new data to be sent.
For this example, assume the “Extra Data Sets” option is set to 02. This increases the amount of
data to 228 bytes. At 300 baud the 228 bytes would take about 7.5 seconds. At 7.5 seconds a
margin of 2.5 seconds is available for preamble, non-data information, and guard time . This
would fit in a 10 second window allowing very little room for drift in the real time clock.
16.7 GOES Binary Data
The self-timed binary transmission and all random transmission formats use a 6-bit per byte
pseudo binary format. The GOES system supports 1, 2, 3, and 4 byte values with 6, 12, 18, and
24-bit precision respectfully. The XL™ will use 3 bytes (18 bits) for the main input data values.
The appended battery voltage will use a single byte (6 bits). The time and date will also use only
one byte each for seconds, minutes, hours, day, and month. However date and time are very
seldom transmitted through the GOES system, and if so, mainly for testing purposes. The
following shows the byte format:
1 Byte Value:
BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
Parity Always 1 DATA 5 DATA 4 DATA 3 DATA 2 DATA 1 DATA 0
3 Byte Value:
BYTE 3 BYTE 2 BYTE 1
23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
P 1 D
17 D
16 D
15 D
14 D
13 D
12 P 1 D
11 D
10 D
9 D
8 D
7 D
6 P 1 D
5 D
4 D
3 D
2 D
1 D
0
Bit 7 is used for parity and will be stripped off by the time the data sent to the decoding software.
Bit 6 always set to ‘1’, forcing the data byte to always be a printable character in the ASCII table.
Valid characters along with there weighted values are listed in the GOES PSEUDO-BINARY
LOOK-UP TABLE on a following page.
Instructions for using the GOES PSEUDO-BINARY LOOK-UP TABLE:
A GOES pseudo binary byte is represented by a single ASCII printable character. All data values
(except battery voltage, time and date) will be made up using three pseudo-binary bytes. To use
the table, look up the weight of each pseudo-binary character using the column according to the