Pseudotetrad
A pseudotetrad (also pseudodecimal ) is a state of a binary coded decimal number (BCD), which is not used (“do n't care ”): Ten states are required to represent a decimal digit, whereby these are four bits (half a byte or . a nibble ), which would thus allow sixteen states. The six unused states are the pseudotetrads.
In normally packed 8-4-2-1 coding, the pseudotetrads correspond to the numbers 10 10 to 15 10 (or A 16 to F 16 or 1010 2 to 1111 2 ). They are used in some systems to encode signs , carries or commas , or they are not used.
In order to minimize Boolean functions (e.g. by means of a KV diagram ), you can decide at will which states of the pseudotetrads are used and which are not. This reduces the circuit complexity z. B. with drivers for seven-segment displays , if no "meaningful" output / display is required for the undefined input values.
BCD table in 8-4-2-1 coding; the entries shaded in dark gray are the pseudotetrads:
| decimal | hexadecimal | binary |
|---|---|---|
| 0 | 0 | 0000 |
| 1 | 1 | 0001 |
| 2 | 2 | 0010 |
| 3 | 3 | 0011 |
| 4th | 4th | 0100 |
| 5 | 5 | 0101 |
| 6th | 6th | 0110 |
| 7th | 7th | 0111 |
| 8th | 8th | 1000 |
| 9 | 9 | 1001 |
| 10 | A. | 1010 |
| 11 | B. | 1011 |
| 12 | C. | 1100 |
| 13 | D. | 1101 |
| 14th | E. | 1110 |
| 15th | F. | 1111 |
The word nibble means Tetrad , in which case the number of bits required is meant.
Individual evidence
- ^ A b c Hans-Jochen Schneider: Lexikon der Informatik und Datenverarbeitung , 2nd edition, R. Oldenbourg Verlag Munich Vienna, 1986, ISBN 3-486-22662-2 .
- ↑ a b c K. Steinbuch, W. Weber: Taschenbuch der Informatik - Volume II - Structure and programming of EDP systems , 3rd edition, Volume 2, Springer Verlag Berlin, 1974, ISBN 3-540-06241-6 .
- ↑ Ambrosius Paul Speiser : Digital Computing Systems - Basics / Circuit Technology / Working Method / Operational Safety , 2nd edition, Springer-Verlag / IBM , ETH Zurich 1965 (1961). LCCN 65-14624, ID 0978.