Difference between revisions of "Binary coded decimal"
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Revision as of 23:22, 16 November 2012
Binary coded decimal (BCD) is a method by which 4-bit numbers are represented in digits 0-9, not 0-F. In the F8, BCD numbers can be added together using ASD or from memory using AMD (there is, however, no AID opcode, BCD Add Immediate). In a single byte, two digits can be stored, and the appropriate carry flags set if the number rolls over 99. Each digit is coded as the number + 6, so 0 should be loaded as 6, 1 as 7, 2 as 8, etc. This table shows the encoding for individual digits:
Digit | 4-bit Value
-------------------
0 | %0110
1 | %0111
2 | %1000
3 | %1001
4 | %1010
5 | %1011
6 | %1100
7 | %1101
8 | %1110
9 | %1111
