Pseudobinary data formats
The pseudobinary data format is a modified-ASCII format that uses the lower 6 bits of each 8-bit data character to represent part of a binary message. To encode a number, its binary form is broken into groups of 6 bits. Each group is placed into the lower 6 bits of a respective byte. The number 64 is added to each byte to set the seventh bit. Binary numbers are transmitted MSB (most significant bit) first.
Pseudobinary formats are preferred for GOES and Meteosat/EUMETSAT self-timed transmissions because users can include more data in the GOES message. This allows more data to be transmitted in a specific window of transmission time.
These messages are not human readable and need to be decoded by computer software or by using custom decoding tables.
Because only 6 bits are used in each byte, the range that a byte or series of bytes can represent is diminished (Pseudobinary ranges).
| Pseudobinary type | Range |
|---|---|
| 1-byte encoded unsigned integer | 0 to +63 |
| 1-byte encoded signed integer | –32 to +31 |
| 2-byte encoded unsigned integer | 0 to +4094 |
| 2-byte encoded signed integer | –2048 to +2047 |
| 3-byte encoded unsigned integer | 0 to +262143 |
| 3-byte encoded signed integer | –131072 to +131071 |
| 4-byte encoded unsigned integer | 0 to +16777215 |
| 4-byte encoded signed integer | –8388608 to +8388607 |